A Life Cycle Assessment of Dehydrated Apple Snacks

Abstract

This study identifies and assesses the main contributors to the environmental impact of dehydrated apple snacks produced through the hot air drying method, which is the most common method for dehydrating food. The study aims to fill the gap of Life Cycle Assessment (LCA) studies regarding dehydrated apple snacks produced using the hot air drying method. A “cradle to gate” approach of an LCA is performed, including the apple production, storage and calibration, peeling and cutting, dehydration, and packaging stages. The inventory used is mainly primary data collected from a fresh and dehydrated apple snacks producer. The results show that the snack producer’s stages have a larger contribution to the majority of categories when compared to the fresh apple producer’s stages. The electricity consumption within the snack production and the use of liquefied petroleum gas in dehydration are shown to be the largest contributors to the majority of the impacts. However, apple production is also shown to have a relevant contribution to the impact categories due to the use of pesticides, fertilizers, diesel, and electricity.

1. Introduction

The agricultural sector has a relevant contribution to the overall environmental impacts associated with food production chains. It is one of the main land users in Europe shaping the rural landscape, and it is largely dependent on the use of natural resources [1]. It also depends heavily on the use of fertilizers and pesticides, which contribute to toxicity-related problems due to air, soil, and water pollution.

In 2021, Portugal produced 2,386,000 tons of fruits and 15% were apples, the second-most produced fruit in the country [2]. However, apples that are not attractive to consumers and do not meet the marketing standard for apples defined by Regulation (EC) No 1619/2001 of 6 August 2001 are considered to be of unsatisfactory quality and thus removed from larger commercial market destinations. An alternative pathway to avoid this is to produce apple snacks through the dehydration of fresh apples. In 2019, the drying and dehydration of fruits and vegetables in Portugal represented 3579 tons and 11.7 million euros and increased when compared to the previous year [3]. Dehydration reduces the water levels of a given product to a level where microbial activity is minimized, preserving the product and reducing its volume [4]. There are several dehydration methods, such as hot air drying, osmotic dehydration, infrared radiation drying, freeze-drying, and microwave dehydration. Hot air drying is the most common method, even though it is known to be an intensive energy-consuming process [5].

A review of the literature shows that numerous articles have studied the dehydration of apples by focusing on drying kinetics, quality parameters, and the use of pre-treatments [4,5,6,7,8,9,10]. Others have studied the environmental impacts of the production of fresh apples. However, only a few studies have assessed the environmental impacts of dehydrated fruits or vegetables.

Table 1. List of reviewed LCA studies concerning apples and other dehydrated food products.

Purpose of the Study, Location, and Timeframe	Functional Unit	Life Cycle Stages Considered	Methodology	Critical Points	Study
Comparative LCA of two options for using rejected apples in Portugal. Timeframe not defined.	1 ha of apple orchard	From gate to gate: storage, dehydration, packaging, and transport.	CML 2 Baseline 2001, CED and Eco-Indicator 99H	Dehydration and packaging, due to the consumption of electricity and natural gas.	[11]
Comparative LCA of drying methods for the production of apple powders. Location and timeframe not defined.	1 package with 3 kg of apple powder	From gate to gate: transport, preliminary stages, dehydration (drum drying or multistage drying), packaging, and distribution.	IMPACT 2002+	Transport, dehydration, storage, and heating.	[12]
Comparative LCA of atmospheric freeze drying with or without ultrasound for granny smith apples, carrot, and eggplant. Location and timeframe not defined.	1 kg of fresh apple	From gate to gate: dehydration.	ReCiPe 2016	Energy consumption.	[13]
Comparative LCA of organic and conventional apples produced in Canada in 2010.	1 ton of fresh apples	From cradle to gate: agricultural production, storage, and transport.	ReCiPe H and UseTox	Fuel use, fertilizer, and pesticide use (for the conventional apple), and electricity spent in storage.	[14]
Comparative LCA of intensive vs. semi-extensive apple orchards in France.	1 ton of fresh apples	From cradle to farm gate.	ReCiPe and CED	Fertilizer production and application.	[15]
Comparative LCA of pistachio, almond, and apple production in Greece from 2011 to 2015.	1 ton of fresh apples	From cradle to gate: irrigation, production of fertilizers and pesticides, production and maintenance of agricultural machinery, field management, post-harvest, and waste management.	CML Baseline 2001	Use of fertilizers and pesticides, and energy consumption.	[16]
Comparative LCA of different apple production systems and productivities.	1 ton of fresh apples	From cradle to gate: fertilization, plant protection and chemical sanitation measures, mechanical work, harvest, and transport.	ILCD	Production of synthetic fertilizers, and energy consumption.	[17]
Comparative LCA of organic and conventional apples produced in Italy. Timeframe not defined.	1 ton of apples packed in 120 kg of carton	From cradle to gate: supply of raw materials and energy, cultivation of apples, post-harvest, and transport.	ILCD 2011	Use of fertilizers and pesticides (for the conventional apple), and use of fuels.	[18]
Comparative LCA of apple and peach produced in Spain. Timeframe not defined.	1 kg of fresh apples	From cradle to gate: cultivation, distribution, consumption, and end of life.	ReCiPe Midpoint (H)	Use of fertilizers and agrochemical substances in agricultural production, and use of energy to store the apple.	[19]
Comparative LCA of conventional and organic apple production systems in China in 2014/2015.	1 ton of fresh apples	From cradle to point-of-sale: agricultural materials, orchard management, and storage and transport.	EDIP 97, CML01 and methods from [25,26,27,28]	Use of pesticides and synthetic fertilizers	[20]
LCA of apples produced in Iran in 2017/2018.	1 ton of fresh apples	From cradle to gate: agricultural production, transport, and storage.	CML 2 Baseline 2000	Energy use and use of fertilizers and pesticides.	[21]
Comparative LCA of potato (including dehydrated potato flakes) and tomato products. Location and timeframe not defined.	1 kg of dried potato flakes	From cradle to grave: agricultural production, dehydration, transport, sale, consumption, and end of life.	ReCiPe 2016 (E) Midpoint	Agricultural production, due to the use of fertilizers and pesticides, and dehydration, due to energy consumption.	[22]
LCA of dried strawberries produced in the United Kingdom in 2016.	450 g of dried strawberries	From cradle to gate: agricultural production, washing and destemming, pre-treatment, freeze-drying, lyophilization, and packaging.	ReCiPe Midpoint	Electricity consumption, use of fertilizers and pesticides.	[23]
LCA of tomato dried in an heat pump dryer in India or in a laboratory-scale microwave dryer in Germany. Timeframe not defined.	1 kg of dried tomatoes	From gate to gate: dehydration.	ReCiPe MidPoint 2014	Energy consumption.	[24]

summarizes the Life Cycle Assessment (LCA) studies of dehydrated agricultural products and the most recent LCA studies on fresh apples. The review comprehends three studies focusing on dried apples [11,12,13], eight on fresh apples [14,15,16,17,18,19,20,21], and three on other dried products (potato flakes, strawberries, and tomatoes) [22,23,24]. The environmental impact assessments of fresh apples showed that production and refrigerated storage are important contributors to their environmental impact. The other studies concerning the dehydration of apples and other foods showed that the dehydration stage has a relevant contribution to the environmental impact due to energy consumption.

The study on an LCA of dried apples in Portugal [11] did not identify the type of dehydration method used and did not assess the impacts of apple production. Moreover, the data for apple storage and dehydration were not from primary sources, but instead retrieved from dehydration prototype equipment using biomass and from the literature published (such as the energy needed for storage). The other studies evaluating apples used a “gate to gate” approach. They either assessed the environmental impacts of drum drying and multistage drying for producing apple powders [12] or used laboratory inventory data to assess the environmental impacts of the ultrasound-assisted atmospheric freeze-drying of food [13].

Our review shows that there are not yet available LCA studies of dried apples using a “cradle to gate” approach or an LCA focusing on the impact of the hot hair drying method, which is known to be the most common method used to dehydrate food worldwide [5]. The present study aims to fill this gap by assessing the environmental impacts of dehydrated apple snacks with a “cradle to gate” approach, using mainly primary data collected from two Portuguese companies, one owning apple orchards and the other producing dehydrated apple snacks through hot air drying. The purpose is to perform a Life Cycle Assessment of dehydrated Golden Delicious apple slices to identify the contribution of the production processes and life stages to the overall environmental impacts. Even though several varieties of apples are produced, the Golden Delicious apple variety accounts for 70% of the apples used by the company to produce dried snacks. Data for the agricultural processes are from a Portuguese company from the Beira-Alta region, with 44 ha of apple orchards. The apple snack production data are from one of Portugal’s main producers of dehydrated fruits. This company currently exports about 40% of its production and, at the beginning of 2022, its brand had a share of 50% of the dried fruit sold in Portugal [29].

In summary, research on the life cycle assessment of apple snacks can contribute to sustainability by promoting responsible consumption and production, reducing waste, improving health outcomes, mitigating climate change, protecting ecosystems, and fostering partnerships. These contributions align with several key Sustainable Development Goals (SDG) from UNEP, making such research an important part of the global sustainability agenda. For example, by identifying the environmental impacts of drying technologies and suggesting impact mitigation measures, this study can contribute to the SDGoals #12 (responsible consumption and production), #13 (climate action), and #17 (partnerships) [30].

2. Materials and Methods

To assess the environmental impacts of the dehydrated apple snacks, we use an attributional Life Cycle Assessment (LCA), as defined by ISO 14040:2006 and complemented by ISO 14044:2006 [31,32]. The assessment is performed using SimaPro PhD version 9.3.0.2 and the database mainly used is Ecoinvent 3.8. For the impact assessment methodology, we use the ReCiPe 2016 Midpoint (H) version 1.06.

2.1. Goal and Scope Definition

The functional unit (FU) is a plastic packaging with 20 g of dehydrated slices of Golden Delicious apple. The system boundaries include the operations comprehending the apple production, calibration and storage, cutting and peeling, dehydration, and packaging (as in Figure 1).

Data for the orchard production are from December 2019—when the agricultural campaign started with the pruning of the trees—and September 2020, corresponding to the harvesting. The timeframe considered for the subsequent stages is between September 2020 and August 2021, which corresponds to the month preceding the subsequent harvest campaign (

Table 2. Time horizon used for the overall primary data collection.

Unit Process	Timeframe
Apple production (orchard)	December 2019–September 2020
Calibration and storage	September 2020–August 2021
Peeling and cutting
Dehydration
Packaging

). Due to the COVID-19 pandemic, in which this timeframe fits, the data may not be fully representative of a period of normal operation because of interruptions in the production process. However, these were the most recent and most complete data available when collecting the inventory data.

The life cycle stages of distribution, consumption, and end-of-life are not evaluated, because no company records are kept from the products leaving the company gates and the end-of-life options for packaging vary according to the behavior habits of the end consumer. Excluded from the study are also all the production, maintenance, and cleaning of equipment, the transportation of the materials used, administrative processes, the cleaning of buildings, and quality control processes. Such exclusions are due to the lack of availability of accurate primary data. The life cycle activities considered are described below:

• Apple production: The integrated production method used in orchard production assures the implementation of good agricultural practices for sustainable production. This is achieved by managing natural resources and prioritizing the use of natural regulation mechanisms, not completely avoiding the use of fertilizers and pesticides, but using modern technology to minimize their use [33,34]. A campaign lasts for about a year and comprehends three stages: pruning, thinning, and harvesting. Pruning consists of removing branches during the winter, changing the form and growth of the tree. Thinning consists of controlling excess flowering to reduce the low-caliber fruits with a low commercial value. The company applies chemical thinning, later complemented by mechanical thinning. The Golden Delicious apple production ends with harvesting, usually in September.
• Calibration and storage: The apples are stored in refrigerated chambers with a controlled atmosphere concerning carbon dioxide and oxygen. The chambers assure the preservation of the apples for up to one year and their temperature is kept between 1 and 2 °C. The calibration involves the use of water to wash the apples, move them and separate them by caliber. The water is treated so that it can be reused. Equipment with a calibration software distributes the apples in sixteen sizes, based on some of the apple characteristics such as weight, color, and existing stains. The company owns electric trucks used to move the apples inside the factory.
• Peeling and cutting: This process begins by washing the apples and selecting the ones that will proceed to the next production steps. Afterwards, apples are automatically peeled and cored and their stalks are removed manually. Then, the apples are manually fed to the laminator to be sliced and go through a conveyor to a water tank where they are washed before going to the dehydration tunnel. The apples rejected and all the other apple residues originated in this stage are sent to be used for animal feed. The water used in this process can either be tap water or well water. The latter is treated with sodium hydroxide 50% and sodium hypochlorite 15% in smaller amounts. Such amounts are not accounted for by the company and therefore not inventoried.
• Dehydration (hot air drying): Dehydration occurs with the continuous circulation of hot air in a dehydration tunnel that runs on Liquefied Petroleum Gas (LPG). The apple slices remain in the tunnel for from 6 to 8 h at 80 °C. In the end, the snacks’ moisture content is less than 2%. The dried apple slices are manually selected according to their size and stored in a cool and dry place. The storage is made using plastic bags and buckets to ensure that the product keeps its quality by not being exposed to air. The bags are not reusable, but the buckets have long lifetimes and are reused after being sanitized. The dried apple slices with the desirable size proceed to the next stage and the ones with a smaller size are used to produce apple flour outside the company boundaries.
• Packaging: The dried apple slices are packed in plastic bags (with three layers: polypropylene, polyester, and polyethylene). The packages go through a metal detector and a scale, and the packages that do not comply with the defined parameters are rejected. In this case, the packages are rejected and the product is repackaged. Packaging waste is also produced due to the calibration of the packaging equipment whenever a new packaging process begins.

2.2. Inventory Analysis

The inventory raw data are supplied from the primary data provided by the two companies from the apple snacks supply chain (fresh apple and apple snack producers). Apple production data are obtained from the records of the diesel used in agricultural machinery, water consumed for irrigation, and electricity used by water pumps and other equipment. To estimate the quantities of diesel, electricity, and well water specific to the Golden apples, it is considered that the consumption of these, by each apple type, is proportional to their share in terms of production area (Equation (1)). The calorific value of 36.9 MJ/L is used to calculate the energy consumption from the diesel burned in agricultural machinery [35].

$${Input}_{Golden}={Input}_{Total}\times \left({Area}_{Golden}/{Area}_{Total}\right)$$

(1)

For the pesticides and fertilizers, the values are obtained from the company records specifically applied to the Golden apple. For pesticides, only the active substances are considered to assess the impacts. The active substance of each product and its concentration are obtained from the technical sheet of the product and their quantities are calculated using their concentration and the quantity of product applied. The emissions to soil, air, and water directly originated from the use of pesticides and fertilizers are estimated. For pesticides, 85% of the substances are emitted to the soil, 10% to the air, and the remaining 5% stays in the leaves [36].

For fertilizers, the nitrogen content is obtained from the technical sheet of the products and the emissions due to its use are calculated based on emission factors from the literature [37,38]. The default emission factor to estimate the direct N₂O emissions to the air is 0.01 kg N₂O-N/kg N applied, and to estimate the NO₃ emissions to the water due to leaching or runoff, 0.30 kg N/kg N is applied [37]. These guidelines define an emission factor for both NH₃ and NO_x emissions, not discriminating the respective emissions of each substance. For this reason, the emission factors used to estimate the NH₃ emissions to air due to volatilization are presented on

Table 3. NH₃ emission factors for N fertilizers.

Fertilizer Type	Emission Factor (% NH3-N Loss of Total Applied N)
Urea	15
Ammonium Nitrate, Calcium Ammonium Nitrate, NP, NK, NPK	2
Ammonium Sulphate	10
Urea Ammonium Nitrate solution	8
Ammonium Phosphate	5

. Values were retrieved from [38]. For urea, an emission factor of 0.2 ton C/ton urea is used [37].

Inventory data for the storage and calibration activities are obtained from the company bills for water and electricity. This may imply that these values may be overestimated, as they include, for instance, the consumption of water and electricity in offices and bathrooms. However, such overestimation is not expected to be relevant in the final impact results. No losses of water are assumed, so the volume of wastewater is identical to the water consumed. To estimate the consumption of water and electricity related only to the Golden apple, the consumption of these by each apple type is considered to be is proportional to its mass production share (Equation (2)). The refrigerated chambers use carbon dioxide, but no company data are available for this consumption.

$${Input}_{Golden}={Input}_{Total}\times \left({Mass}_{Golden}/{Mass}_{Total}\right)$$

(2)

Inventory data from the peeling and cutting process are obtained from the daily records of the volume of tap water and well water consumed. The water consumption is entirely accounted to this process, even though it also includes the water consumed in the pantry and sanitary facilities. But this amount is expected to be a negligible fraction of the total volume of water used. According to the company data, about 35% (w/w) of the apple is peel, core, and stalk. This value is used to obtain the quantity of apple slices at the end of this process (Equation (3)).

$${Mass}_{apple slices}={Mass}_{Golden apple}\times \left(1-0.35\right)$$

(3)

Inventory data from the dehydration process are collected through the company’s records of the consumption of LPG and polyethylene bags and records detailing which product was produced each day. The estimation of the LPG used considers the daily averaged values measured by the company and the number of days when apple slices were dehydrated. The energy value of 45 MJ/kg is used to calculate the energy from the burning LPG [39].

Inventory data from the packaging are retrieved from company records. The mass of each component of the plastic film is estimated based on the packaging technical data sheet. The packaging consists of polypropylene, polyester, polyethylene, and adhesive with, respectively, weights of 18, 17, 46, and 1.5 g/m². The mass of each component i is calculated using Equation (4).

$$m_i=m_{plastic film}\times \frac{{weight}_i}{18+17+46+1.5}$$

(4)

The electricity consumption is obtained from daily internal records for the electricity consumption from the national electricity grid and from the monthly records of the solar energy produced by the apple snacks company. The electricity from the solar panels is calculated to be about 19% of the overall electricity consumed. Electricity consumption occurs along all the apple snack production stages, but it is not possible to differentiate the electricity used in each activity. It includes the electricity consumed by the refrigerated storage of apples in summer, the electric forklift truck, the cutting and peeling equipment, the ventilation of the tunnel hot air dryer (dehydration), the packaging equipment, the compressed air system, the industrial air conditioning used to keep an optimum temperature for product preservation, the office equipment, and the industrial plant illumination.

Table 4. Inventory data for the life cycle activities of apple snacks, including apple production, processing to dehydrate snacks, and packaging. All values report to the FU (a pack with 20 g of dehydrated apple slices).

Apple Production—Inputs	Unit	Value
Land used	ha	6.12 × 10−6
Diesel used in agricultural machinery	MJ	9.08 × 10−2
Electricity	kWh	3.54 × 10−2
Well water	m3	1.20 × 10−2
Fertilizers
Urea	kg	4.28 × 10−5
Ammonium Nitrate, Calcium Ammonium Nitrate, NP, NK, NPK	kg N	1.56 × 10−5
Ammonium Sulphate	kg N	9.79 × 10−6
Urea Ammonium Nitrate solution	kg N	4.61 × 10−6
Pesticides
Abamectin 1	kg	8.81 × 10−8
Captan	kg	2.94 × 10−5
Carfentrazone-ethyl 1	kg	1.47 × 10−7
Chlorantraniliprole 1	kg	2.45 × 10−7
Copper 1	kg	1.96 × 10−5
Cyprodinil 1	kg	2.51 × 10−6
Difenoconazole 1	kg	8.41 × 10−7
Dithianon 1	kg	5.74 × 10−6
Flonicamid 1	kg	4.28 × 10−7
Fluxapyroxad 1	kg	1.10 × 10−6
Fosetyl	kg	1.14 × 10−5
Glyphosate	kg	1.32 × 10−5
Mancozeb	kg	1.88 × 10−5
Metiram 1	kg	1.71 × 10−5
Milbemectin 1	kg	7.02 × 10−8
Paraffin oil 1	kg	1.58 × 10−4
Potassium phosphanates	kg	2.57 × 10−5
Pyriproxyfen 1	kg	3.06 × 10−7
Spirotetramate 1	kg	7.34 × 10−7
Sulfur 1	kg	5.88 × 10−5
Tetraconazole 1	kg	2.45 × 10−7
Thiophanate-methyl 1	kg	4.28 × 10−6
Triflumuron 1	kg	7.34 × 10−7
Apple Production—Outputs	Unit	Value
Golden apple	kg	2.79 × 10−1
Emissions to soil (due to the use of pesticides)
Abamectin	kg	7.49 × 10−8
Captan	Kg	2.50 × 10−5
Carfentrazone-ethyl	kg	1.25 × 10−7
Chlorantraniliprole	kg	2.08 × 10−7
Copper	kg	1.66 × 10−5
Cyprodinil	kg	2.13 × 10−6
Difenoconazole	kg	7.15 × 10−7
Dithianon 2	kg	4.88 × 10−6
Flonicamid	kg	3.64 × 10−7
Fluxapyroxad	kg	9.36 × 10−7
Fosetyl	kg	9.70 × 10−6
Glyphosate	kg	1.12 × 10−5
Mancozeb	kg	1.60 × 10−5
Metiram	kg	1.46 × 10−5
Milbemectin	kg	5.96 × 10−8
Paraffin oil	kg	1.35 × 10−4
Potassium phosphanates	kg	2.19 × 10−5
Pyriproxyfen	kg	2.60 × 10−7
Spirotetramate 2	kg	6.24 × 10−7
Sulfur	kg	4.99 × 10−5
Tetraconazole	kg	2.08 × 10−7
Thiophanate-methyl	kg	3.64 × 10−6
Triflumuron	kg	6.24 × 10−7
Emissions to water (due to the use of fertilizers)
Nitrate	kg	1.49 × 10−5
Emissions to air (due to the use of pesticides)
Abamectin	kg	8.81 × 10−9
Captan	kg	2.94 × 10−6
Carfentrazone-ethyl	kg	1.47 × 10−8
Chlorantraniliprole	kg	2.45 × 10−8
Copper	kg	1.96 × 10−6
Cyprodinil	kg	2.51 × 10−7
Difenoconazole	kg	8.41 × 10−8
Dithianon 2	kg	5.74 × 10−7
Flonicamid	kg	4.28 × 10−8
Fluxapyroxad 2	kg	1.10 × 10−7
Fosetyl	kg	1.14 × 10−6
Glyphosate	kg	1.32 × 10−6
Mancozeb	kg	1.88 × 10−6
Metiram	kg	1.71 × 10−6
Milbemectin 2	kg	7.02 × 10−9
Paraffin oil	kg	1.58 × 10−5
Potassium phosphanates	kg	2.57 × 10−6
Pyriproxyfen	kg	3.06 × 10−8
Spirotetramate 2	kg	7.34 × 10−8
Sulfur	kg	5.88 × 10−6
Tetraconazole 2	kg	2.45 × 10−8
Thiophanate-methyl	kg	4.28 × 10−7
Triflumuron	kg	7.34 × 10−8
Emissions to air (due to the use of urea)
Carbon dioxide	kg	3.14 × 10−5
Emissions to air (due to the use of fertilizers)
Ammonia	kg	4.62 × 10−6
Nitrous oxide	kg	4.97 × 10−7
Storage and Calibration—Inputs	Unit	Value
Golden apple	Kg	2.79 × 10−1
Tap water	L	1.99 × 10−1
Electricity from electric grid	kWh	5.30 × 10−2
Storage and Calibration—Outputs	Unit	Value
Golden apple	Kg	2.79 × 10−1
Wastewater	L	1.99 × 10−1
Peeling and Cutting 3—Inputs	Unit	Value
Golden apple	kg	2.79 × 10−1
Tap water	L	3.41 × 10−5
Well water	L	1.32 × 10−3
Sodium hydroxide	kg	1.23 × 10−5
Peeling and Cutting—Outputs	Unit	Value
Apple slices	kg	1.82 × 10−1
Apple co-products	kg	1.10 × 10−1
Wastewater	L	1.35 × 10−3
Dehydration 3—Inputs	Unit	Value
Apple slices	kg	1.82 × 10−1
Polyethylene (PE)	kg	4.13 × 10−4
Liquefied petroleum gas (LPG)	kg	4.53 × 10−2
Energy generated from the liquefied petroleum gas	MJ	2.04 × 10+0
Dehydration—Outputs	Unit	Value
Dehydrated apple slices	kg	2.03 × 10−2
Apple co-products	kg	4.73 × 10−4
Plastic waste	kg	4.13 × 10−4
Packaging 3—Inputs	Unit	Value
Dehydrated apple slices	kg	2.03 × 10−2
Polypropylene (PP)	kg	9.91 × 10−4
Polyester (PET)	kg	9.36 × 10−4
Polyethylene (PE)	kg	2.53 × 10−3
Solvent less adhesive 2	kg	8.26 × 10−5
Packaging—Outputs	Unit	Value
Pack of dehydrated apple slices (FU)	kg	2.40 × 10−2
Apple co-products	kg	3.05 × 10−4
Plastic waste	kg	5.33 × 10−4

¹ No specific life cycle inventory database was available. Impacts modelled by considering the database for the production of unspecified pesticides. ² Impact not calculated due to the absence of an adequate inventory database. ³ These activities have overall an electricity consumption of 0.341 kWh (from the electric grid corresponding to about 81% of the overall consumption) and 0.080 kWh (from the solar panels which sums up 19% of the total consumption). Both values report to the functional unit.

shows the inventory data for apple production, calibration and storage, peeling and cutting, dehydration, and apple snacks’ packaging. All values are reported to the functional unit.

Given the gaps in the LPG records and the variability in the values of the LPG consumption, and given the uncertainty of the CO₂ emission factor associated with the application of urea (−50% uncertainty [37]), the influence on the results of the variation in these parameters is also evaluated. The values considered are in

Table 5. Values considered for the parameters that have shown a large variability or uncertainty.

Parameters	Value
Liquefied Petroleum Gas	Minimum	0.101 kg/F.U.
	Maximum	4.53 kg/F.U.
CO2 emission factor (use of urea)	−50%	0.1 ton C/ton urea

.

3. Results and Discussion

3.1. Environmental Impacts

Figure 2 shows the activities’ contributions for the 17 environmental impact categories assessed. The peeling and cutting stage (represented with the grey color) has a negligible contribution to all the impact categories assessed (less than 1%) and thus not visible in Figure 2. The absolute values and percentage of the contributions are shown in the Supplementary Material (Table S1). Overall, the electricity consumption (at the apple snacks producer) is the activity with the largest contribution to the majority of the impact categories. The results show a larger contribution to nine categories (varying from 39% to 50%). Then, the dehydration and apple production stages are shown to have the larger contribution to four categories. The contribution ranges from 37% to 63% for dehydration and from 63% to 85% for apple production. Apple production stands out with a contribution of over 80% for three impact categories (water consumption, land use, and terrestrial ecotoxicity). Each life-cycle stage is assessed in more detail below, from the most significant contributors to the less.

3.1.1. Electricity Consumption

The electricity consumption of the snack producer considers 19% of solar energy and 81% of the electricity mix from Portugal which, in 2021, was 59% from renewable sources [40]. The contribution of this consumption to the overall environmental impact is mainly due to the use of electricity from the national electric grid. This process has the largest contribution to the environmental impact categories of ozone formation—human health, fine particulate matter formation, ozone formation—terrestrial ecosystems, terrestrial acidification, freshwater eutrophication, marine eutrophication, marine ecotoxicity, human carcinogenic toxicity, and human non-carcinogenic toxicity.

The contribution to categories such as marine ecotoxicity, human carcinogenic toxicity, and human non-carcinogenic toxicity is mainly due to the use of the spoil from hard coal mining extraction (used to produce electricity) that is contaminated with toxic heavy metals and, therefore, the use of more renewable energies would reduce the impacts originated from this toxicity. The use of more energy-efficient technologies would reduce the overall environmental impact of the electricity consumption.

3.1.2. Dehydration

Then, the dehydration stage shows the largest contribution to the environmental impact categories of global warming (51%), stratospheric ozone depletion (45%), mineral resource scarcity (37%), and fossil resource scarcity (63%). Fossil resources and their combustion are the main contributors to those impacts, as the dehydration stage uses exclusively LPG. This stage has a high contribution to the environmental impact because the dehydration method used is a thermal drying method, with significant thermal losses during the heat transfer to the apple slices due to the air’s low thermal conductivity. Other non-thermal methods or conductive heat transfer in a solid medium with a higher thermal conductivity (such as drum drying) may be a solution to mitigate the impact from this process [30].

The dehydration and electricity consumption are two of the most concerning activities. This supports some observations made in the literature, where the authors say that hot air drying is characterized by a high energy consumption [5,30].

3.1.3. Apple Production

Apple production has a larger contribution to the categories of water consumption, land use, freshwater, and terrestrial ecotoxicity. The emissions from the application of fertilizers and pesticides are the main contributors to the impacts on terrestrial and freshwater ecotoxicities. Such emissions are also the main contributors to marine eutrophication and marine ecotoxicity. For the remaining categories, the main contributors are the use of diesel, electricity consumption, and pesticides production.

3.1.4. Calibration and Storage

The stage of calibration and storage is the subsequent stage in terms of contribution, despite not being the larger contributor in any of the categories. The larger contribution to the marine eutrophication category, when compared with other categories, is due to the wastewater produced in this stage.

3.1.5. Packaging

Packaging contribution to the environmental impact varies from 0.4% to 9.5%. This impact is mainly due to the use of low-density polyethylene in the packaging film, due to the larger share in mass used. The packaging has a significant impact on the water consumption category, due to the large amount of water used in plastic production. The use of alternative materials for packaging and a reduction in the package size may be solutions to mitigate the impact from this stage.

3.1.6. Peeling and Cutting

The peeling and cutting stage has a negligible contribution to all the impact categories assessed, due to the small amounts of sodium hydroxide and water. The amount of water here used represents less than 1% of the water consumed at the apple production (to irrigate) and at the calibration and storage (to wash and transport the apples) stages. Therefore, this life-cycle stage was not shown to have a large contribution.

3.2. Influence of the LPG and the Variation of the CO₂ Emission Factor on the Results

Table 6. Results obtained for changes in the LPG values (considering the minimum and maximum). Results are reported to the base case results.

Impact Category	LPG Min	LPG Max
Global warming	−30%	+62%
Stratospheric ozone depletion	−27%	+55%
Ionizing radiation	−13%	+27%
Ozone formation, Human health	−19%	+38%
Fine particulate matter formation	−18%	+37%
Ozone formation, Terrestrial ecosystems	−19%	+39%
Terrestrial acidification	−17%	+35%
Freshwater eutrophication	−19%	+39%
Marine eutrophication	−7%	+13%
Terrestrial ecotoxicity	−5%	+10%
Freshwater ecotoxicity	−7%	+14%
Marine ecotoxicity	−13%	+27%
Human carcinogenic toxicity	−19%	+38%
Human non-carcinogenic toxicity	−12%	+25%
Land use	−4%	+9%
Mineral resource scarcity	−22%	+44%
Fossil resource scarcity	−38%	+77%
Water consumption	−1%	+2%

shows the results obtained for the cases where minimum and maximum LPG values were used to assess its influence on the overall impact results (values shown in Table 5). The variation in the CO₂ emission factor (indicated in Table 5) led to no changes in any of the impact categories assessed, meaning that this value did not influence the results obtained.

Not surprisingly, results show that the variation in the LPG consumed changes significantly the values obtained for the environmental impact categories. A change in the value for LPG consumption results in changes in the impact results that go from −38% to +77% (in relation to the base case). The largest variation found is observed for the fossil resource scarcity category.

3.3. Comparison of GWP Results with the Previously Reviewed Studies

A comparison of the results obtained with the studies previously reviewed (shown in Table 1) allows observing that the most critical activities in terms of the contribution to the environmental impact in the present study are similar to those mentioned in the literature. They include the use of fertilizers, pesticides, electricity, and diesel of the apple producer and the consumption of electricity and LPG of the snack producer. In this section, due to different methods chosen to assess the impacts, a comparison among results was performed only for the GWP. To ease the comparison,

Table 7. Comparison with studies focusing on the apple dehydration methods. Results obtained are expressed in terms of mass (ton) of fresh apples.

Study	Global Warming Potential (kg CO2 eq./ton Fresh Apple)	Drying Method (Inventory Data Used for Impact Modelling)
This study	1306 (min = 857; max = 2219)	Hot air drying (industrial data, process fueled by LPG).
[13]	129,000–318,000	Ultrasound-assisted atmospheric freeze-drying (used data from a non-industrial process—mathematical model).
[12]	212–383	Drum drying and multistage drying (industrial data, fueled by natural gas).
[11]	209	Not identified (used a prototype fueled by biomass with a 70% efficiency).

and

Table 8. Comparison with studies focusing on fresh apple. Results obtained are expressed in terms of mass (ton) of fresh apple.

Study	Global Warming Potential (kg CO2 eq./ton Fresh Apple)	Observations
[17]	66	Integrated production. Does not include calibration and storage.
[16]	89	Production type not defined. Includes only temporary storage before going to a warehouse.
[15]	75–90	Intensive and semi-extensive production. No electricity is accounted for. Storage is not assessed.
This study	178	Integrated production.
[14]	276–283	Conventional and organic production. Includes storage and distribution.
[19]	302	Integrated production. Includes storage, packaging, consumption, and disposal.
[18]	588–612	Conventional and organic production. Includes distribution to final consumer, which contributes with about 40% to GWP, and storage.
[20]	865–957	Conventional and organic production. Includes storage, distribution, and bagging of the apples to protect them from bird biting and pest infestation. Intensive use of non-renewable energy in the production of pesticides, fertilizers, and paper bags.
[21]	3009	Production type not defined. Includes storage and transport from orchard to refrigerator (300 km). Intensive use of diesel (1348 L/ha compared to 260 L/ha obtained in this study) mainly used in irrigation.

present the values for the GWP reported to 1 ton of fresh apple.

Table 7 presents the results obtained by only considering the snacks producer’s stages. The results do differ when compared to the studies from the literature [11,12,13]. Concerning the present study, it is recognized that the dehydration method used is widely used in food dehydration and is an intensive energy user. The results for the GWP express the energy consumption to produce apple snacks by including the ventilation of the hot air dryer tunnel, the compressed air system, and the industrial plant’s air conditioning system. Despite not having disaggregated company data for the individual processes, it is expected that the contribution of the ventilation of the hot air tunnel occupies a maximum share of 40% of the overall consumption (this value was communicated personally to the authors by the snack producer in 2023). The difficulty of the comparison of this work’s results with the literature values is because none of the studies used industrial data from a dehydration process (hot air drying) specifically used for apple snack production. Drum and multistage drying are specific for apple powder production and may not apply to apple snacks’ production. Moreover, one of the other studies [11], despite focusing on snack production, made use of biomass as an energy source for dehydration, making a comparison with the results from the present study not possible.

Table 8 presents the gathered data for the apple producer’s stages (apple production and calibration and storage). It is observed that the GWP values vary within a wide range. Such variation is mainly due to the assessment or not of processes such as storage, calibration, and transport. In addition to this, the company owning the orchard follows an integrated production [33,34], and thus, the amounts of fertilizers and phytopharmaceuticals are rationalized when compared to the reviewed studies making use of conventional production.

The calibration and storage stage are shown to have a relevant contribution to the apple producer’s GWP (mainly from the storage step due to its energy consumption). Such contribution equals 42.5% of the overall GWP of apple production (Table S1). However, studies [15,17] did not mention any storage step in the assessment and [16] assessed a system designed for temporary storage. When calculating the GWP for the present study by not considering the contribution of the calibration and storage stage, the GWP is 76 kg CO₂ eq./ton fresh apple. Such a value is similar to the ones from the above-mentioned studies.

The remaining studies include transport, different cultivation practices (such as the bagging of apples), or a larger share of non-renewable energy, leading to higher results for the GWP.

4. Conclusions

This study fills in the gap of available LCA studies on apple snacks produced by making use of the most used dehydration method (hot air drying). This is achieved by performing a transparent, comprehensive, and detailed impact assessment. Such an LCA was made using data from cradle to gate collected from two companies from the snack production value chain (apple producer and snacks producer). The representativeness of the inventory data is revealed by the fact that, currently, the company data supplier has a large share of the dried fruit sold in Portugal and exports about 40% of its production.

The performed comprehensive life cycle environmental assessment (from cradle to gate) of dehydrated apple snacks shows that the production of snacks has a larger contribution than the production of fresh apples. The apple snacks production contributes from 14% to 91% to the environmental impact, being the larger contributor for 13 of the 17 impact categories assessed. The energy needed to produce the dried snacks is the most critical point of snacks production. In the snacks production, the dehydration process is the most critical process, with a large consumption of LPG and electricity used to ventilate the drying tunnel. For the apple production, the use of pesticides, fertilizers, and diesel in the orchard and the electricity used for storage are the most critical aspects. The land and the water used also represent relevant contributions to the environmental impact.

Some limitations to the work carried out are either related to a lack of company data or to the inventory databases available in SimaPro. The absent data associate with the carbon dioxide used by the refrigerated chambers, the gaps in the registration of the LPG used in the dehydration, and the non-discrimination of the electricity spent by each activity, while limitations found for the modelling relate to the lack of adequate databases for the production and emissions of some pesticides and the snacks’ packaging adhesive. To overcome such gaps, it is recommended to perform regular and accurate measurements of company input data, especially for LPG consumption, due to its importance (as seen in Table 6) to the impacts results.

The comparison of the results obtained in this study with the ones from the reviewed literature is limited due to the different dried products, dehydration methods, data sources, processes, and activities considered. Despite this, the comparison of the results with other studies (Table 8) shows that integrated production may lead to smaller contributions to environmental impact. For the production of snacks, it was observed in previous studios performed on dehydration methods that the hot air drying method is an intensive energy consumer and the results obtained are larger than the results from the literature.

For future research work, the literature suggests alternative technologies that may be less impactful than conventional hot air drying technology. Some of the technologies that could lead to a mitigation of the environmental impact include refractance window drying, microwave drying, drum drying, ultrasound-assisted drying, and heat pump drying [30,41]. The literature also suggests some adaptations to the hot air drying method that may reduce its impact. For example, the combination of ultrasound with hot air drying may have advantages, namely, potentially reducing the dehydration time and energy consumption and better preserving the characteristics of the fruit [6]. In addition, the use of desiccant dehumidification primarily powered by solar thermal collectors may be also one way to decrease the energy consumption based on the fossil fuel used in the snacks drying tunnel [42]. These alternatives should reduce the consumption of energy, the most critical aspect of the dehydrated apple snacks’ life cycle. A Life Cycle Assessment study of these alternatives and studies on the quality of the product resulting from using such alternative technologies will assist in verifying its real influence on the environmental impact and the feasibility and adequacy of the use of the technologies to produce dehydrated apple snacks.