Lye Peeling Research Articles

Demonstration Tests of Infrared Peeling System with Electrical Emitters for Tomatoes

. Infrared (IR) dry-peeling is an emerging technology that could avoid the drawbacks of steam and lye peeling of tomatoes. The objectives of this research were to evaluate the performance of an IR peeling system at two tomato processing plants in California and to compare product quality, peelability, and energy consumption of IR and steam peeling. The system was continuously operated using tomatoes of different sizes and cultivars. High percentages (62% to 85%) of fully peeled tomatoes were obtained and varied depending on tomato cultivar and seasonality. IR dry-peeled tomatoes had a firmer texture than steam and lye peeled tomatoes. IR peeling achieved a peeling loss in the range of 17% to 42%, which was lower than typical loss in the industry. Small tomatoes had higher loss than large tomatoes in the late season. Thermal energy consumption of the proposed technology in full-scale production (10 ton h-1) is predicted to be 117.0 and 137.3 MJ ton-1 for indoor and outdoor operation, respectively. The estimated energy savings of IR dry-peeling should be 22% and 28% compared to lye and steam peeling, respectively. The demonstration results showed that the IR dry-peeling technology could be a viable alternative to lye and steam peeling.

Tomato peeling by ohmic heating with lye-salt combinations: Effects of operational parameters on peeling time and skin diffusivity

Ohmic heating without lye has shown promise in tomato peeling; however the use of lye is known to yield high peeled-product quality. In this work, we studied the operational parameters of the ohmic peeling process, specifically, the influence of salt-lye concentration combinations and field strength on time for skin cracking during ohmic peeling. We further investigated the influence of electric fields on the lye diffusivity through tomato skin. The treatments of 0.01/0.5% NaCl/NaOH at 1610 V/m and 0.01/1.0% NaCl/NaOH at 1450 V/m were the conditions that required the shortest time for cracking. For NaCl/KOH mixtures, 0.01/0.5% NaCl/KOH at 2020 V/m and 0.01/1.0% NaCl/KOH at 1450 V/m required the shortest time for cracking. Studies on diffusion through the tomato skin showed that ohmic heating significantly improved lye diffusion (p < 0.05) at both 50 and 65 °C. After an initial period, diffusivities of lye peeling with ohmic heating were greater than those without ohmic heating at both 50 and 65 °C, confirming that the electric field enhances diffusion of NaOH through the tomato skin.

Tomato peeling by ohmic heating: Effects of lye-salt combinations and post-treatments on weight loss, peeling quality and firmness

Ohmic heating without lye has shown promise in tomato peeling; however the use of lye is known to yield high peeled-product quality. This investigation was aimed at determining whether a combination of ohmic heating and low lye concentrations could be synergistic. The results indicated that 0.01/0.5% NaCl/KOH at 2020 V/m was the best condition for tomato peeling in terms of quality, weight loss, and peel cracking time. Further, the treatment showed weight loss that was not significantly different from conventional lye peeling at 7% NaOH and 7% KOH (p < 0.05). NaCl/NaOH mixtures also showed good results, but the quality of products was lower than that using the same concentration, but a higher field strength with NaCl/KOH mixtures. However, no improvement was found using NaCl/CaCl2 and NaCl/NaOH/CaCl2 mixtures which were also found difficult to use due to turbidity and cleaning difficulties. A post-peeling treatment by ohmic heating was investigated to improve firmness of ohmically peeled tomatoes. It was found that the best conditions were 2% CaCl2 solution at a field strength of 403 V/m for 1 and 5 min, and 484 V/m for 5 min. Industrial Relevance Our earlier work had shown that ohmic heating resulted in peeling of tomatoes that were immersed in salt solutions. The current work details the impact of using small concentrations of lye (either sodium or potassium hydroxide) on peeling loss and quality. Also, we investigate the potential use of calcium chloride, both as peeling solution or as a post-peeling infusion as it impacts firmness of tomatoes. We show that there are ranges of operating conditions which provide yield and quality comparable to conventional lye peeling at far lower lye concentrations, resulting in potentially significant environmental benefit to companies currently using lye peeling.

Efficacy of various techniques on biochemical characteristics and bitterness of pummelo juice.

The consumer acceptability of pummelo juice is affected badly due to the presence of bitter principles in it. Therefore in order to avoid such bitterness development, the extracted juice from pummelo was subjected to five different treatments like juice diffused into syrup (70°Brix), lye peeling of segments in boiling NaOH for 2-3min, increasing the pH of juice, hot water treatment (50°C) prior to peeling for 20min and without any treatment (control) for suppressing the development of bitterness in the juice. Based on bio-chemical analysis, diffusion of juice into syrup (70°Brix) showed better result as compared to other treatments. The maximum amount of TSS was found in juice diffused into syrup (i. e. 45, 30 and 15°Brix) along with highest TSS/acid ratio (92.21, 49.87 and 17.53). Higher amount of acidity was observed in pH adjusted samples with 4.25, 4.50 and 4.75 respectively. However, control samples showed higher amount of ascorbic acid (73.97mg/100ml juice) content followed by pH adjusted samples. The highest organoleptic score for taste (8.00), colour (8.83), aroma (8.66), overall acceptability (7.88) and extent of debittering (7.50) were recorded in juice diffused into syrup 70°Brix and achieved final TSS of juice at 45, 30 and 15°Brix respectively. Moreover, the above treatment (juice diffused into syrup 70°Brix) showed promising low cost and easy to adopt technique of debittering in respect of extent of debittering and maintaining sensory quality during storage of pummel juice.

Evaluation and Optimization of Steam and Lye Peeling Processes of Sweet Potato (Ipomea batatas) using Response Surface Methodology (RSM)

Abstract Sweet potato of uniform sizes and shape were subjected to steam peeling (temperature 80–100°C and peeling time 5–15 min) and lye peeling (sodium hydroxide concentration 8–12%, temperature 80–100°C and peeling time 3–5 min). Response surface methodology was used to analyze and optimize the process parameters in each case. For steam peeling, the peel loss and unpeeled surface area were 6.85 and 28.16%, respectively, while optimum peeling conditions where temperature and peeling time of 100°C and 5 min, respectively, for minimum peel loss and unpeeled surface area. For lye peeling, however, the peel loss and unpeeled surface area were 13.19 and 13.35%, respectively, and optimum peeling conditions were lye concentration, temperature and peeling time of 8.89%, 100°C and 4.75 min, respectively, for minimum peel loss and unpeeled surface area. The models developed in each case (R-squared of 0.9225 and 0.8428; 0.5929 and 0.8346) were adequate in producing responses as a function of the independent variables. From the optimized values and results obtained, lye peeling was more suitable for sweet potato.

Peeling of tomatoes using novel infrared radiation heating technology

Abstract The effectiveness of using infrared (IR) dry-peeling as an alternative process for peeling tomatoes without lye and water was studied. Compared to conventional lye peeling, IR dry-peeling using 30 s to 75 s heating time resulted in lower peeling loss (8.3%–13.2% vs. 12.9%–15.8%), thinner thickness of peeled-off skin (0.39–0.91 mm vs. 0.38–1.06 mm), and slightly firmer texture of peeled products (10.30–19.72 N vs. 9.42–13.73 N) while achieving a similar ease of peeling. IR heating increased the Young's Modulus of tomato peels and reduced the peel adhesiveness, indicating the tomato peels to loosen, become brittle, and crack more easily. Also, IR heating resulted in melting of cuticular membrane, collapse of several cellular layers, and severe degradation of cell wall structures, which in turn caused peel separation. These findings demonstrated the effectiveness of the novel IR dry-peeling process for tomatoes. Industrial relevance Development of a sustainable and non-chemical peeling technique for food processing industry is urgent. Currently, industrialized peeling methods such as hot lye or steam peeling are water- and energy-intensive operation and result in a large amount of waste effluent. Disposal of these wastewater containing high salinity and organic solids poses negative environmental footprints. Tomato processors have long been interested in pursuing a sustainable and non7 chemical peeling alternative in order to minimize waste effluent containing high salinity and organic loads and reduce the negative environmental impacts associated with conventional hot lye peeling. The emerging infrared dry-peeling technique offers a novel approach to eliminate the usage of chemicals and water in the peeling process while maintaining high quality peeled products. The study explored several crucial and fundamental aspects of developing infrared radiation heating technology as a sustainable tomato peeling method. The findings of this research provide scientific evidence of the benefits of infrared dry-peeling in comparison to the conventional hot lye peeling and have been used for the development of a pilot scale tomato infrared dry-peeling system.

A comparison of dynamic mechanical properties of processing-tomato peel as affected by hot lye and infrared radiation heating for peeling

This study investigated the viscoelastic characteristics of tomato skins subjected to conventional hot lye peeling and emerging infrared-dry peeling by using dynamic mechanical analysis (DMA). Three DMA testing modes, including temperature ramp, frequency sweep, and creep behavior test, were conducted to evaluate the transition temperatures and dynamic moduli of tomato peels heated by infrared radiation and hot lye at four heating durations (30, 45, 60, and 75s). Fresh tomato peels were used as a control. Results showed that dynamic moduli of tomato peels were sensitive to temperature ramp and frequency sweep tests. Over a temperature range from 20°C to 100°C, transition temperatures of infrared treated peels (63–72°C) and lye treated peels (43–75°C) were significantly lower than those of fresh control (∼88°C). Values of both storage and loss moduli of infrared heated peels were considerably higher than those of the fresh control, whereas values of the storage and loss moduli from the lye peeled samples were lower than those of fresh peels. DMA tests effectively differentiated the viscoelastic behaviors of tomato peels and indicated mechanistic differences between the lye peeling and infrared dry-peeling.

Conventional and Alternative Methods for Tomato Peeling

Peeling is one of the most important unit operations in tomato processing. Most recently, three novel tomato peeling methods were reported: infrared, ohmic heating and power ultrasound. Steam/hot water and lye peeling have been the most commercialized methods, but compared to steam peeling, lye peeling is more preferred and has gained widespread application among processors due to its association with higher product yields and better product quality. However, with the ever-tightening environmental protection laws, concerns have arisen in the recent years regarding lye usage as well as its disposal, which calls for alternative chemical-free peeling methods that can effectively peel the tomato while minimizing peeling losses and improving product quality. This review highlights the conventional methods used in tomato peeling, their efficacy and the potential applications of infrared, ohmic heating and power ultrasonics as a novel technology for tomato peeling.

Effects of food processing on food allergens

Food allergies are on the rise in Western countries. With the food allergen labeling requirements in the US and EU, there is an interest in learning how food processing affects food allergens. Numerous foods are processed in different ways at home, in institutional settings, and in industry. Depending on the processing method and the food, partial or complete removal of the offending allergen may be possible as illustrated by reduction of peanut allergen in vitro IgE immunoreactivity upon soaking and blanching treatments. When the allergen is discretely located in a food, one may physically separate and remove it from the food. For example, lye peeling has been reported to produce hypoallergenic peach nectar. Protein denaturation and/or hydrolysis during food processing can be used to produce hypoallergenic products. This paper provides a short overview of basic principles of food processing followed by examples of their effects on food allergen stability. Reviewed literature suggests assessment of processing effects on clinically relevant reactivity of food allergens is warranted.

Technical Note: Development of Infrared Radiation Heating Method for Sustainable Tomato Peeling

Although lye peeling is the widely industrialized method for producing high quality peeled fruit and vegetable products, the peeling method has resulted in negative impacts by significantly exerting both environmental and economic pressure on the tomato processing industry due to its associated salinity issues and wastewater disposal problems. The objective of this research was to develop alternative peeling methods with reduced or no caustic usage to produce high quality peeled tomatoes. The feasibility of using infrared radiation (IR) peeling and lye-IR peeling as alternative technologies was evaluated against control treatment which used regular lye peeling alone. Peeling performance and peeled tomato quality of three tomato cultivars were determined. The metrics for peeling performance were peelability, peeling easiness, and peeling weight loss. The color and texture of peeled tomatoes were measured as quality indicators. The study showed that IR peeling resulted in a similar peeling easiness but yielded lower peeling loss and firmer peeled product for the same or slightly longer peeling time when compared to regular lye peeling method. Pretreatment with low concentration of lye solution prior to IR treatment did not show any advantages over IR peeling alone. Because IR dry-peeling produced high quality product without using water and salts, it is concluded that it has a good potential as an alternative peeling method to the regular lye peeling method.

Pilot Scale Processing of Red Flesh Guava RTS Beverage

Pilot scale studies on production of ready-to-serve (RTS) beverage from red flesh guava were done using 100 kg of the fruit. Pulp yield was more (73.68 %) in lye peeling than in hand peeling (58.68 %). RTS beverage was prepared by mixing fruit pulp with syrup to an optimum level of acidity and sugar, as standardized on a laboratory scale. Blending RTS beverage by using colloidal mill improved the colour, consistency and overall quality. From 100 kg of red flesh guava, 247 litres of RTS beverage could be obtained. The cost:benefit ratio and value addition from this process were worked out at 1.79 and Rs. 5.45/kg of fruit, respectively.

POTASSIUM HYDROXIDE REPLACEMENT FOR LYE (SODIUM HYDROXIDE) IN TOMATO PEELING

Lye (sodium hydroxide [NaOH]) peeling is the most common method for peeling tomatoes in the Midwest U.S. With the rise in the cost of NaOH and the associated disposal problems, alternative methods for peeling need to be examined. Solutions of NaOH, potassium hydoxide (KOH) and calcium hydroxide (Ca[OH] 2 ) at different concentrations were compared to determine their efficacy as peeling agents. Ca(OH) 2 was ineffective as a peeling agent because of its low solubility. KOH produced peeling equivalent to NaOH, but at half the normality. A lower normality is needed because of the increased reactivity of KOH compared to NaOH. This is further demonstrated by the addition of salts to the solution. The use of KOH instead of NaOH may result in cost savings and decreased waste disposal problems.

Lye Peeling of ‘Tombul’ Hazelnuts and Effect of Peeling on Quality

Hazelnuts were lye peeled and the peeling time (2–12 min), temperature (63–97°C) and NaOH concentration (40–140 g NaOH kg –1 peeling solution) effects on peeling and quality were investigated. Increases in both temperature and concentration of lye solution led to a decrease in peeling time. Moisture content of samples were changed significantly ( P –1 peeling solution, 94.9°C and 2.9 min peeling time. This combination resulted in peeling > 98%, 0.45 mm penetration depth, 7.1 g titratable NaOH kg –1 and a Hunter-L value of 52.93. The quality parameters of peeled hazelnuts at this given combination, such as protein, oil, free fatty acid, ash contents, peroxide number and L values showed no significant change if compared with untreated control samples.

Processing‐induced changes in total phenolics and procyanidins in clingstone peaches

AbstractClingstone peaches contain a wide array of complex secondary plant metabolites and polyphenolics, and increasing evidence indicates that many of these components are important in human health. Oligomeric flavan‐3‐ol metabolites (procyanidins) are particularly interesting owing to their potent antioxidant activity and protective cardiovascular effects. To date, little information is available on how postharvest and processing conditions impact levels of phenolics and procyanidins in fruit. This research addresses the impact of lye peeling, freezing, storage temperature (4 and 30 °C) and three different time–temperature sterilisation combinations on levels of total phenolics (TPs) in Ross clingstone peaches. Additionally, we describe the profile of procyanidin oligomers (monomers through heptamers) in clingstone and freestone peaches and demonstrate a dramatic decrease in procyanidins in thermally processed peaches. TP levels ranged between 316 and 397 mg kg−1 in peeled peaches and between 376 and 609 mg kg−1 in unpeeled peaches. Cold storage at 4 °C for 14 days or freezing and storing at −12 °C for 3 months produced no loss in TPs. Peaches stored at 30 °C for 24 h resulted in a 1.7‐fold increase in TPs. Studies of TPs in peaches processed at temperatures of 213 °F for 40 min, 220 °F for 10 min and 230 °F for 2.4 min indicate that processing above 213 °F decreases levels of both TPs (up to 21%) and procyanidins (up to 100%). Processing at 213 °F for 40 min produced no significant loss in TPs. Furthermore, studies reveal that a 30–43% loss in phenolic levels occurs during the first 3 months in storage after canning. It is clear that both storage and thermal processing conditions profoundly impact the levels of polyphenolics in peaches. More interestingly, these studies indicate that peaches are a rich source of procyanidins, having profiles similar to those found in cocoa, apples, wine and tea.© 2002 Society of Chemical Industry

Effects of high hydrostatic pressure or high intensity electrical field pulse pre-treatment on dehydration characteristics of red paprika

The effects of various pre-treatments (hot water blanching, skin treatments, high pressure and high intensity electric field pulse treatment) on the dehydration characteristics of red paprika ( Capsicum annuum L.) were evaluated and compared with untreated samples. Hot water blanching (100°C, 3 min) prior to dehydration (fluidised bed dryer at 60°C, 6 h and 1 m/s) resulted in the permeabilisation of 88% of the cell membranes in paprika, which in turn resulted in a higher mass and heat transfer. Skin treatments (such as lye peeling and acid treatment), as practised conventionally, increased dehydration rates but affected only the skin permeability. The application of high hydrostatic pressure (HHP, 400 MPa for 10 min at 25°C) or high intensity electric field pulses (HELP, 2.4 kV/cm, pulse width 300 μs, 10 pulses, pulse frequency 1 Hz) pre-treatments resulted in cell disintegration indexes of 0.58 and 0.61, respectively. Cell permeabilisation of these physical treatments resulted in higher drying rates, as well as higher mass and heat transfer coefficients, as compared to conventional pre-treatments.

TREATMENT of TOMATO LYE PEELING WASTEWATER BY FERRIC CHLORIDE COAGULATION and FILTRATION

The suspended solids, soluble and insoluble COD, and particle size were measured for lye peeling wastewater from the tomato industry. The wastewater was treated by conventional coagulation techniques using ferric chloride as a coagulant. Acidification and carbonation were compared as methods to lower the pH. Jar testing was done using a pH level of 9-13 and coagulant levels of 8. 6-51 mg/L The most effective coagulation was achieved at a coagulant dose of 26 mg/L at a pH level of 9 resulting in an average residual turbidity reduction of 92%. Coagulation significantly reduced the insoluble solids (60%), but had no significant effect on dissolved organic matter, thus total COD was only decreased by 14.5%. Filtration had no effect on the suspended or dissolved solids in wastewater.

Technological Processes To Decrease the Allergenicity of Peach Juice and Nectar

Among vegetable foods peach (Prunus persica) has been recognized as a significant cause of allergy. The protein, which is considered to be the major peach allergen, has been named Pru p 1. Because peaches are consumed both as fresh fruits and after processing to obtain peach juice, nectar, jam, syrupy peach, etc., research was carried out to identify a technological process for production of hypo- or nonallergenic peach-based products. SDS-PAGE and immunoblotting analysis of extracts prepared from four commercial peach nectars showed that the Pru p 1 was not removed, and neither was its allergenic activity decreased by technological treatments carried out for nectar production. Some treatments oriented toward a removal of or, at least, a decrease in the allergenic power were assumed and verified at laboratory scale. A variable considered was heat treatment at 121 degrees C for 10 and 30 min: this treatment was not able to decrease the allergenicity of the Pru p 1 protein. Furthermore, the protein band was still present even after 60-min reaction with two different acidic proteases. The two technological treatments that were found to decrease the major allergen of peach were chemical lye peeling of fruits and ultrafiltration of juice through membranes with suitable cutoff. On the basis of the results obtained from this research, a processing flow sheet was defined to obtain hypoallergenic or probably nonallergenic limpid juices and nectars. These products may represent, besides finished foods, intermediates to obtain various products after addition of further ingredients such as pectins, sugars, and fiber.

USE of ORGANIC SOLVENTS FOR IMPROVING PEELABILITY of TOMATOES

A prepeeling dip was used to demonstrate that removal or modification of the cuticular waxes from the tomato fruit could be used to improve the tomato peeling process. the tomatoes were dipped at various temperatures for I min prior to regular lye peeling. the optimum temperature was found to be 45C. Several organic solvents including chloroform, ethyl acetate, ketones, and alcohols were used. These tomatoes were compared to tomatoes peeled using the lye without the dip. the prepeeling dip reduced the thickness of the cuticular wax layer and produced cracks in the cutin surface. This facilitated good penetration of lye into the tomato resulting in more complete peeling. Peeling after pretreatment produced 86% well peeled tomatoes as compared to 33% well peeled in the control run.

Color of Minimally Processed Potatoes as Affected by Modified Atmosphere Packaging and Antibrowning Agents

ABSTRACTMinimal processing of potatoes was studied by using different treatments of cut potatoes in combination with modified atmosphere packaging. Different packaging materials and peeling methods were evaluated. An L‐cysteine (0.5%) and citric acid (2%) mixture prevented browning of potatoes effectively. Active modification of the atmosphere inside the package was necessary to achieve extended shelf‐life. Nitrogen flushing was more effective than other gas treatments with a highly permeable multilayered polyolefin packaging material. Hand peeling and lye peeling resulted in better quality, but abrasion peeling was undesirable for fresh potatoes. The shelf‐life of the minimally processed products could be extended to nearly 3 wk under refrigerated storage.

Mathematical analysis of lye peeling of tomatoes

Time-temperature-concentration relations for lye peeling of tomatoes were investigated and a mathematical model was developed and tested. The time-temperature correlation was linear, while the time-concentration correlation was exponential. Two sets of treatments were used in the experiments: (a) treatment with sodium hydroxide alone; and (b) pretreatment with sorbic acid followed by immersion in sodium hydroxide. Treatment with 9% sodium hydroxide at 90°C for 60 s was sufficient to peel the tomatoes. The model developed predicted the results with a correlation coefficient of approximately 0·99.