Oven Drying Research Articles

Evaluation of the environmental performance of the production of polyphenol-rich fruit powders: A case study on acerola

This study evaluated the environmental performance by life cycle assessment (LCA) of five popular drying processes (freeze drying, spray drying, spouted bed drying, convective hot air oven drying, and foam mat drying) to obtain polyphenol-rich acerola powders from acerola juice and pomace. To the best of our knowledge, this is the first report in the literature showing the total polyphenol content (TPC) as the target quality index to evaluate the LCA of fruit-based dried ingredients, taking the potential functionality into consideration. Acerola powders had low moisture content (1.43%–5.20%) and water activity (0.301–0.433), and remarkably high TPC (79–287 mg GAE/g). LCA results showed that the re-purposing of readily available and burden-free pomace is a smart and eco-friendly solution to secure polyphenol-rich fruit powders with lower environmental impact (<10%) and resource availability (<50%). On the contrary, juice-derived powders have higher potential ecological impact associated to agricultural cultivation. Oven drying exceeded in 75–80% the impact to the ecosystems of other drying processes, which jeopardizes process viability. Drying attributes that dictate environmental performance were identified, such as powder productivity and carrier selection, with maltodextrin having >60% lower impact than albumin in 9 out of 10 mid-point categories evaluated. High powder productivity (35.8 g/h and 34.7 g/h for juice- and pomace-derived powders, respectively) and robustness endorse spray drying as an eco-minded drying strategy for the efficient processing of naturally polyphenol-rich materials. This research provides comprehensive data to support the upcycling of fruit pomaces as smart feedstocks to produce phytochemical-rich food ingredients.

PHYSICOFUNTIONAL PROPERTIES OF EGG POWDER AS INFLUENCED BY DRYING METHODS

The study was carried out to determine the physical and functional properties of whole egg powder produced using four drying methods. Twenty (20) trays of freshly laid eggs were obtained from Shika brown layers at 27 weeks at lay. The eggs were alloted into four drying methods (sun, air, oven and dehydrator drying).Each 500grams of liquid egg produce a range of 122 – 125grams of egg flask which were grinded for 5min egg at a speed of 10,000Rm and sieved using a 0.5mm. A powder of 120grams was produce from each batch of 500grams of liquid and a total 1200grams of powdered eggs were obtained for each of the methods. 2 grams of each samples in a replicate of three using a complete randomize design (CRD) was collected and used for physical and functional properties of whole egg powder. The results of the study show there were significant difference across all the parameters measured except for gelation, colour absorbance and particle size The Functional properties of the powder differs (P &lt; 0.05) across all the drying methods except for emulsion capacity, gelation and oil absorption stability. Dehydrator and air-dried egg powder were better than oven and sun dried egg powder in most of the physical and functional properties determined. It is concluded that egg powder can be produced using any of the process method tested but air drying gives optimize overall properties while oven drying happen to be the least among the methods. It is recommended that egg powder should be produce using air drying method.

Unlocking peach juice byproduct potential in food waste biorefineries: Phenolic compounds profile, antioxidant capacity and fermentable sugars

This work assesses an integrated pathway for the revalorization of peach byproduct (PB) within a biorefinery. PB was subjected to an oven-drying (OD) treatment for its evaluation as a storage treatment. It was compared to freeze-drying and untreated material in terms of antioxidant capacity (AOC), phenolic compounds (PC) profile and fermentable sugar production. OD reduced the water content to less than 15 % while preserving the bound hydrolysable polyphenols, which were the more abundant PC (≈64 %) with the highest AOC. Drying treatments hampered polysaccharide accessibility, but some enzyme preparations released 60–70 g/L of fermentable sugars at relatively high solids loading (10 %). This study proposes a novel enzyme-based strategy for the valorisation of fermentable sugars and antioxidant compounds from PB. The sugars can be fermented into several building blocks while the solid residue enriched in recalcitrant phenolic compounds and proteins could be used to develop novel functional products for food/feed sectors.

Utilization of dried dairy cow feces as biogas substrate and biogas sludge as organic soil conditioner

Utilization of farm waste as an alternative energy source is a form of farm waste management, but field applications are not optimal. The purpose of this study is to find out to what extent the dried dairy cow feces can function as a biogas substrate for an overview of the number of anaerobic bacteria, the volume of bio-gas, and the use of organic carbon-containing biodiesel mud so that it can be used as an organic soil fertilizer. This study uses an experimental research method and looks at the results of an independent T test with two treatments: sundry and dry oven. The tests were done on days 0 (after 4 hours), 7, 14, 21, and 28. The water level, number of bacteria, volume of gas, and pH and organic C content of the biogas sludge were all recorded. The study's findings showed that the number of anaerobic bacteria on days 0 (after 4 hours), 7, 14, 21, and 28 and the amount of biogas on days 14 and 21 did not change whether the samples were dried in the sun or in a furnace. However, on days 7 and 28, the amounts of biogas changed depending on whether the samples were dried in the sun or in a furnace.

Effect of Drying Methods on the Moisture Content and Microbiological Properties of Three Varieties of Dried Onion Slices (Allium cepa)

Post-Harvest losses of onions occurring due to poor handlings and spoilage by microorganisms is worthy of concern. Value addition through drying during peak seasons can reduce losses remarkably. This study sought to evaluate the effects of different drying methods on the microbial load of dried onion slices. Three varieties of onion (red, white and cream) were purchased National Institute for Horticultural Research (NIHORT) Kano sub-station and processed into dried slices using three dryers namely; Solar Cabinet Dryer (SCD), Electric Powered Dryer (EPD) and Kerosene Powered Dryer (KPD) at three different temperatures (50, 60 and 70oC). The dried onion slices were then evaluated for their microbial load; Aerobic Plate Counts (APC), Coliform Counts (CC) and Fungal Counts (FC) using three different media and according to standard methods. The results revealed that MC of onions were reduced from 88.29% to as low as 5.19% during drying. The APC, CC and FC of red onion ranged from 3.67–5.39×102 cfu/g, 1.35–5.39×102 cfu/g and 3.44–4.83×102 cfu/g respectively. The load for white onion ranged from 3.11–5.19×102 cfu/g, 1.31–5.29×102 cfu/g and 3.43–4.53×102 cfu/g respectively while that of cream onion ranged from 3.30–5.33×102 cfu/g, 1.33–5.39×102 cfu/g and 3.42–4.57×102 cfu/g respectively. All the readings fell below the international recommended safe limit for food consumption. The EPD samples at 60oC and 70oC had the significant lowest (p≤0.05) fungal counts in all the onion varieties. Therefore, electric oven dryer at 70oC was the best drying methods and temperature for onion for long time storage.

Unlocking the potential of pomegranate peels as a valuable source of bioactive compounds through effective drying strategies

Pomegranate peels are a great resource of bioactive compounds that have potential for various applications, including functional foods, pharmaceuticals, and cosmetics. However, the drying process is an important consideration that can affect the quality and properties of pomegranate peels. This investigation sought to assess the results of different drying procedures that affect the physicochemical, functional, and antioxidant properties of pomegranate peels. Four alternative drying techniques were used such as freeze drying, microwave drying at 900 W, oven drying at 50 °C, and sun drying. According to the findings, the freeze-drying method exhibited the highest total phenolic content (186.24 mg GAE/g DM), DPPH radical scavenging activity (77.86 %), vitamin C (77.5 mg AA/100 g DM), and ferric reducing antioxidant power (31.1 mg AAE/g DM). The sun-drying technique, on the other hand, had the lowest level of quality parameters. The oven and microwave drying methods exhibited comparable results. These findings provide essential information for the optimization of pomegranate peel drying conditions, enhancing its potential to use as a significant source of bioactive compounds for a range of industrial applications. The freeze-drying method is recommended for preserving the quality of pomegranate peels and can be applied in various industries to produce high-quality products.

Optimization of Total Phenolic Content from Gynura Procumbens Leaves Under Oven and Microwave Drying

The optimization of the process variable; temperature, power, and drying time, under oven and microwave drying were studied for total phenolic content of Gynura procumbens leaves. The optimization conducted using response surface methodology central composite design of experiment. The optimum drying condition was obtained at 65.61°C at 10 hours with 201.78 mgGAE/g of TPC yield for oven drying while, for microwave drying was 436.19 Watt at 8.37 minutes with 12.24 mgGAE/g of TPC yield. The response surface methodology used in this study was able to predict the optimum drying condition for total phenolic content via linear and interaction mathematical model with higher adjusted coefficient determination , for both oven and microwave drying, 0.9383 and 0.7785, respectively. Hence, the models gave good prediction of the total phenolic content obtained from Gynura procumbens leaves under the experimental conditions used in this study. In addition, these outcomes are also expected to contribute to the production of shelf stable Gynura procumbens leaves which can be used for pharmacological purposes.

The Effect of Processing on Some Nutritional Indices of Purple Onion, (Allium cepa Linn), Bulb

Onion (Allium cepa L.), also referred to as “Queen of the kitchen”, is a common vegetable that is widely consumed all over the world. It is has peculiar taste, unique flavor, highly valued aroma, and various health benefits. This all important condiment however, has a short shelf life which is a major cause of postharvest losses during the peak of harvesting season. Scarcity resulting from the losses has led to a thought of its processing with the aim of retaining its medicinal and nutritional properties. The present study was therefore, aimed at evaluating the effect of processing on the Vitamins and Minerals composition of purple onion using two processing methods (sun drying (SD) and oven drying (OD) at 70oC), compared to fresh samples. These Parameters were evaluated using standard Biochemical methods. The results obtained showed that all the parameters tested were affected significantly (P˂0.05) by oven drying process when compared to the fresh sample. The Vitamins (A, B1, B2, B3, B6, B9, C, and E,) composition showed an increasing composition of the parameters in the order of Fresh ˂ SD ˂ OD. From the foregoing, it can be suggested that oven drying (70oC) is an efficient method of processing and preservation of purple onion. The results from the study could be a direction towards the promotion of preservation of purple onions and an encouragement of the industrialization of the process of producing onion powders, which is readily available in all seasons and meet consumer requirements.

Analysis of carcass weight and proximate composition as guinea pig [Cavia porcellus (Linnaeus, 1758)] meat quality indicator

Guinea pig (GP) meat [Cavia porcellus (Linnaeus, 1758)] can serve as an alternative food due to its high protein content. GP is the staple food in Peru, thus tropical regions (Indonesia) can cultivate it. GP can be purchased at animal markets for an acceptable cost. Carcass weight and proximate analysis are required to evaluate GP meat characteristics. To examine the impact of frozen storage on meat quality, this study aimed to compare GP meat quality with chicken and catfish. The frozen meat was from commercial markets. The methodology comprised meat selection, carcass weight, proximate evaluation, and data analysis. The hind leg, thigh, and tail sections of GP, chicken, and catfish, respectively, were used for proximate evaluation and evaluated using the Titrimetric method, the Weibull method, the Oven Drying method, ash calculation, the By Difference method, and meat tenderness test. Regarding carcass weight, GP has the lowest weight. However, it has the finest proximate analysis results, compared to catfish and chicken, with a protein value of 17.42%. GP meat has potential to be gained as a high-protein food source at a reasonable cost. As opposed to chicken and catfish, more portions of GP can be consumed as meat.

Drying Efficiency of Betung Bamboo Strips (Dendrocalamus asper) Based on Different Solar Drying Oven Designs

Drying Efficiency of Betung Bamboo Strips (Dendrocalamus asper) Based on Different Solar Drying Oven Designs

Cost-effective process development for sericin recovery from silk degumming wastewater

Sericin is a silk protein gum that draws attention due to recovery opportunity from textile effluents since it has anti-bacterial, anti-cancer, anti-UV and moisture absorption properties. This study investigates the development of a cost-effective process for the recovery of sericin from silk degumming effluents that would contribute to closing the technical and economical gaps in the field of resource recovery. The cost of sericin recovery was initially calculated by evaluation of capital and operational costs based on pilot and lab-scale tests. Eight alternatives from A1 to A8, covering combinations of pre-treatment (flocculation/sedimentation), volume reduction (nanofiltration-NF), solidification (ethanol precipitation + centrifugation) and drying (lyophilization, spray drying or oven drying) steps were considered to find the optimum recovery cost that would be competitive with the commercial price of sericin. Total costs were estimated to be between €140,000 and €2,600,000 for a plant lifetime of 15 years. The unit cost of recovered sericin was estimated to vary significantly from €89 to €1300 per kg. Alternatives A6 (pre-treatment + NF + oven drying), A7 (pre-treatment + oven drying), and A8 (pre-treatment + NF) enable competitiveness with market prices. For these alternatives, staff and energy expenditures were the main cost items. The payback period can be reduced from 15 years to 5 years by increasing the unit price of recovered sericin by 5%–30%. The developed cost-effective process would form a novel basis for a circular business model for the recovery of sericin as well as other resources such as nutrients, water, and energy.

Physical Quality of Lemongrass Powder (Cymbopogon citratus L.) From Microwave Oven Drying

Serai dapur (Cymbopogon citratus L.) dapat dikenal sebagai tanaman herbal yang memiliki banyak manfaat. Selain itu, serai dapur juga dapat digunakan untuk memberikan cita rasa yang khas pada suatu masakan. Penggunaan serai pada suatu makanan dapat dilakukan secara langsung dalam keadaan segar ke dalam masakan. Penggunaan serai dapur dalam bentuk yang segar dapat dikatakan kurang praktis dan tidak dapat disimpan dalam waktu yang lama. Hal yang dapat dilakukan untuk memperpanjang masa simpan serai salah satunya adalah dengan cara mengolah serai segar menjadi bubuk serai. Oleh karena itu, salah satu penanganan yang tepat untuk memperoleh mutu produk dengan kualitas baik dan mengurangi kerusakan yaitu dengan cara melakukan proses pengeringan menggunakan microwave. Tujuan dari penelitian ini adalah untuk mengetahui mutu fisik bubuk serai dapur hasil pengeringan microwave dan mempelajari hubungan daya microwave dan durasi penepungan yang berbeda terhadap mutu fisik bubuk serai dapur. Hasil penelitian menunjukan kadar air serai segar berkisar 85,928 – 87,208 % sedangkan kadar air bubuk serai dapur berkisar 5,876 – 9,728%. Serai dapur yang sudah melalui proses pengeringan dan penepungan selanjutnya dilakukan proses pengayakan menggunakan ayakan 60 mesh. Bubuk serai dapur yang lolos ayakan kemudian diukur mutu fisiknya. Mutu fisik bubuk serai dapur yang dihasilkan yaitu mutu fisik bubuk serai yang dihasilkan yaitu memiliki tingkat kecerahan (L) berkisar antara 78,48-90,87 ; tingkat kemerahan (a) berkisar antara -0,49 sampai – 1,45; tingkat kekuningan (b) berkisar antara 0,22 – 3,62; densitas curah berkisar antara 0,41 – 0,48 g/cm3; aktivitas air berkisar antara 0,33-0,40. Berdasarkan hasil analisis statistik, mutu fisik bubuk serai dapur dengan kombinasi perlakuan terbaik diperoleh pada perlakuan perbedaan daya microwave.

Study the effect of drying methods On the quality characteristics for dill and parsley

This research studied the effects of three drying methods (solar, electric oven, microwave) and two different drying duratiqcontent (%), drying rate (kg/h), and dry matter color. The experiment werer conducted in the Medicinal Plants Laboratory at the College of Agricultural Engineering Sciences, University of Baghdad, for the winter season of 2022/2023. The goal of the experiment was to determine the best drying method for dill and parsley plants that would give the best quality for each of them. Thirty-six samples were randomly divided into 6 groups (3 for dill and 3 for parsley). Each group of one plant was dried using one of the three studied drying methods. Each group was further divided into two parts (three samples each) with different drying durations (first duration, second duration). The results showed that Parsley had a lower moisture content (81.86%) compared to dill (83.67%), suggesting that parsley is more resistant to moisture loss than dill. The microwave drying had the lowest moisture content (80.69%) and the highest in electric oven drying (84.02%). For the drying rate, the highest value (0.01378 kg/h) was observed in dill, while the lowest rate (0.0115 kg/h) was in parsley. Drying methods had a significant effect on the drying rate, with the microwave method having the highest rate (0.113 kg/h) and the electric oven method the lowest (0.011 kg/h) .The microwave drying resulted in a significantly shorter drying duration compared to electric oven and solar drying, with a reduction of 5.6% and 6.4%, respectively. The drying methods showed a significant difference in terms of color, with the highest color value of 8 observed in the microwave drying method and the lowest value of 7.17 in the solar drying method. The electric oven drying method had a color value of 7.83, indicating that microwave drying preserved color quality. The drying duration did not have a significant effect on the studied parameters.

Design and Performance Evaluation of a Novel Solar Dryer for Drying Potatoes in the Eastern Algerian Sahara

Abstract In this paper, experimental work has been presented to study the novel design of a solar crop dryer that includes an inverted absorber perforate type collector with forced airflow. A novel design configuration was constructed and tested in the eastern Algeria climate (El Oued city) for drying potatoes. We aimed to present a test of the thermal performance of the novel dryer and use only clean energy sources for evaluating the drying efficiency. Under real climatic conditions, the experimental test indicated that the average air temperature of the drying chamber is 50 °C, and the time required for drying potatoes starting at the initial moisture content (MC) of 84.17% until the final MC of 12.5% is 6h. The highest specific moisture extraction rate value was obtained as 1.074 g water/kWh. The drying efficiencies ranged from 20.37% to 34.01%, whereas the exergy efficiency ranged from 58.48% to 93.22%. The payback period was estimated as 1.39 years. The proposed novel dryer will dry potatoes free of cost for almost its entire life period, and about $13.92 can be saved. Compared with electric oven drying, the novel one has the following advantages: the cost of electricity saving and avoiding penalty tax for CO2 emission were $11.69 and $2.235, respectively.

Microwave exposure of tomato varieties before catalytic oven drying and its effect on physicochemical and bioactive components studied by Fourier transform infrared (FTIR) spectroscopy

This study investigates the microwave-oven drying process to dehydrate two tomatoes (Solanum lycopersicum) varieties for the enhancement of its quality. Roma and grape tomato slices were pre-dried using microwave power densities of 10, 15 and 20 W, respectively for 10 min before catalytic hot-air oven drying temperature at 60 °C for 8 h. The dried tomato slices were cooled and milled into powder. Physicochemical, bioactive, phytonutrients, colour, textural and fourier transform infrared spectroscopy (FTIR) characterization of the dried grape and Roma tomato were carried out according to standard method. Decrease in the pH of the microwave pre-dried tomato slices was accompanied by significant increase (p < 0.05) in the total titratable acidity as the microwave power densities increased. The ascorbic acid value increased significantly (p < 0.05) with increasing power densities for Roma tomato while colour profile reduced. The phenolic compounds decreased with a corresponding increase (p < 0.05) in total carotenoid, lycopene and beta-carotene in Roma tomato variety. Majority of the textural properties decreased with increased in power densities. FTIR revealed the presence of diverse functional groups ranging from alkanes, alcohols, quercetin, aldehydes and phenolic compounds in all the samples evaluated. This study revealed that pre-dried process using microwave at varied power densities retained some of the quality characteristics of dried tomato. Thus, application of microwave power densities prior to oven-drying process could serve as an alternative method towards commercialization of good quality dried tomato for the agro-food processing industry.

Influence of Infill Level and Post-Processing on Physical Parameters and Betaine Content of Enriched 3D-Printed Sweet Snacks.

Betaine is a non-essential amino acid with proven functional properties and untapped potential for cereal food enrichment. While 3D printing represents a viable approach for manufacturing enriched cereal-based foods with novel shapes and textures, it is crucial to consider the impact of printing parameters and post-processing on the betaine content and properties of these products. The aim of this study was to investigate the influence of the infill level (20, 30 and 40%) of 3D-printed cuboid shapes and the post-processing techniques (drying oven, vacuum dryer, air fryer) of betaine-enriched oat-based snacks on the print quality, texture, and sensory properties, as well as the content of preserved betaine. The interaction of post-processing technique and infill level influenced the length deviation and texture properties, as well as the betaine content of snacks. Height stability was only influenced by post-processing technique. In general, oven-dried snacks showed the best dimensional stability, having the lowest width/length deformation (about 8%) at the infill level of 20%. Betaine was best preserved (19-31% loss) in snacks post-processed in a vacuum dryer (1281-1497 mg/g), followed by an air fryer and a drying oven, where betaine loss was in the range 28-55%. Air-fried snacks with 40% infill level had the highest values of instrumentally measured crunchiness (38.9 Nmm) as well as sensory test values for liking of texture (7.5), intensity of odor (6) and overall flavor (6). Overall, air frying proved to be a convenient and quick post-processing technique for 3D-printed snacks, but infill patterns for preserving betaine should be further explored. Vacuum drying could be used to preserve bioactive compounds, but efforts should be made to minimize its negative impact on the physical deformations of the 3D-printed products.

Occurrence of aflatoxigenic fungi and aflatoxins in maize grains and associated awareness and handling practices among farmers and traders in South Sudan

Maize is a popular staple food among the urban population of South Sudan. However, due to inadequate food safety surveillance and enforcement systems, there is limited information on the aflatoxin safety of maize grains at farm and market levels. Therefore, this study aimed at assessing aflatoxins awareness and handling practices of maize grains among randomly selected farmers (n=30) and traders (n=30) as well as determining the moisture content, Aspergillus species counts and aflatoxins contamination. A cross-sectional descriptive study was carried out in Magwi maize producing areas, Juba retail/wholesale markets and Nimule border points of South Sudan. Moisture content, fungal and aflatoxins contamination in maize grain samples were determined using dry air oven method, dilution plating technique, and High-Performance Liquid Chromatography (HPLC), respectively. The respondent results showed that farmers (97%) and traders (83%) were unaware of aflatoxins. About 83% of the farmers dried their maize grains on tarpaulins, for 4 - 5 days (77%). In addition, most farmers (77%) stored their maize grain bags on raised platforms, whereas most traders (73%) stored grains on bare ground. All the maize grains met the required moisture content limit (below 13.5%). Maize from Nimule main park had the highest levels of contamination with Aspergillus flavus (9 log CFU/g), Aspergillus parasiticus (12 log CFU/g), aflatoxin B1 (505.56 µg/kg) and total aflatoxins (1,032.19 µg/kg). Maize from Gudele market was contaminated with Aspergillus parasiticus (12 log CFU/g), and aflatoxin B1 (76.55 µg/kg), and had a total aflatoxin content of 94.09 µg/kg. Omeo farmers’ maize grains had the least levels of contamination of Aspergillus parasiticus (6 log CFU/g), aflatoxin B1 (4.39 µg/kg), and total aflatoxins (7.83 µg/kg). In addition, Aspergillus flavus was not detected from Omeo farmers’ maize grains and no aflatoxins were detected from Agoro and Paluonganyi farmers’ grains. This study recommends wider aflatoxins awareness and regular aflatoxin screening of maize grains by the relevant stakeholders in South Sudan. Key words: aflatoxins, aflatoxigenic fungi, awareness, farmers, handling practices, maize, South Sudan, traders

Study on Three-dimensional Impinging Jet Flow and Heat Transfer of Dryer for Gravure Printing and Coating Machine

Drying system is the largest energy consumption of equipment parts of solvent-based printing and coating equipment. How to optimize to design the equipment is of the highlights of this research field. According to this demand, a mathematical model of fluid flow of the drying oven is developed. By building a testing platform and using RNG k-epsilon two-equation turbulence model in Fluent Software to analyze three-dimensional impinging jet flow and heat transfer process of hot air drying in conventional drying oven. The results show that the separation of some boundary layers and undesirable swirls, which result in the non-uniform velocity field and temperature field of hot air from nozzles and no promotion to the drying effect, because of unreasonable design of the drying oven.

Quality and flavor characteristics evaluation of red sea bream surimi powder by different drying techniques.

The present study investigated the effects of five different drying methods, namely hot-air drying (HAD), cold-air drying (CAD), microwave combined oven drying (MCOD), infrared radiation drying (IRD) and vacuum freeze drying (VFD) on the physicochemical properties and flavor of red sea bream surimi. The L* value of the VFD treatment group (77.17) was significantly higher compared to other treatments (P<0.05). The TVB-N content of the five surimi powder remained within an acceptable range. A total of 48 volatile compounds were identified in surimi powder, with the VFD and CAD groups exhibiting superior odor and taste characteristics, as well as a more a more uniformly smooth surface. The gel strength (4402.00g.mm) and water holding capacity (92.21%) of rehydrated surimi powder in CAD group were the highest, followed by the VFD group. In conclusion, CAD and VFD can be considered as an effective technique for preparing surimi powder.

Postharvest drying of walnuts: Effect of drying methods on walnut quality

It has been demonstrated that drying can significantly promote the antioxidant active substances of fresh walnut, as well as enhance lipid content and conversion of glycerol phospholipids to lysophospholipids in walnut. Currently, oven drying (OD) and natural air drying (NAD) are the two most commonly used drying methods for walnut. However, the differences in their effects on the quality of the final product remain unclear. This study investigated the effect of OD and NAD on the phenotypic and physiological properties and lipid oxidation of four main walnut varieties W10, W179, W185, X2 in Xinjiang, China, and determined the correlations among these properties. The results showed that OD could maintain plump and yellowish white kernels, whereas NAD led to noticeably darker and more wrinkled kernels at the end of drying. In addition, an analysis of quality-related metabolites revealed that two representative lipids PC (18:2_18:2) and PC (18:1_16:0) had completely different patterns under OD and NAD, and the metabolites highly relevant to these two lipids were mainly enriched in amino acid and ascorbate metabolism pathways. Comprehensive physiological and metabolite analysis indicated that OD outperforms NAD in maintaining walnut quality, and may be applied to industrial walnut drying.