drying methods

A study was undertaken the effect of pretreatments and drying methods on quality parameters of tomato slices with respect to storage using two factors as treatments i.e. 5 pre-treatment levels (P1-Peeled by hot water dip blanching, P2-Peeled by hot brine dip blanching, P3-Unpeeled by hot water blanching, P4-Unpeeled by hot brine blanching, P5-Control- No peeled and no blanched) and 2 drying methods i.e. (D1-Tray drying, D2-Sun drying) with completely randomized design of factorial concept with three repetitions at Post Graduate Laboratory of Horticulture Department, College of Agriculture, Junagadh Agricultural University, Junagadh. The quality was evaluated on the basis of physicochemical (i.e. drying time (h) and moisture content (%) at 1, 20, 40, 60 and 80th day of storage. Result of study depicts that the pretreatment P2 i.e. peeling of tomato by hot brine dip blanching followed by tray drying (D2) recorded minimum (14.50 h) drying time and the minimum changes in moisture content (4.00%-6.54%) observed in treatment P1 at 1st to 80th day of storage, respectively.

Effect of drying methods (sun-drying and cabinet oven drying) on the physicochemical properties and fatty acid composition of oils extracted from moringa seeds was investigated. Oil from the seeds was extracted using solvent (hexane) after drying. Drying increased the yield from 30.30-33.11%. The oil samples were less dense than water with specific gravities of 0.9032, 0.9075 and 0.9030 respectively. A significant difference exists in the moisture contents (0.11-0.21%); smoke point (202-2250C), flash point (310-3170C) and fire point (360-3690C). Sun-drying and cabinet oven drying brought about a decrease in the acid value (1.80-1.08mgKOH/g), saponification value (174.87-105mgKOH/g), Iodine value (16.10-13.90wijs) and peroxide value (11.24-2.3-Meq/kg). The decrease is an indication of quality improvement of the oils. More unsaturated fatty acids were present in the samples between 76.61% and 81.66%. Oleic acid was predominant (44.92% raw, 45.71% sundried and 43.60% cabinet oven dried). Sun-drying and cabinet oven drying did not have much significant effect on the physical, chemical and fatty acid compositions of the oil. The results obtained from this study showed that the three oil samples are good as edible oil and for commercial purpose.

This study was carried out to evaluate the effect of pretreatments and drying methods on the chemical quality and microbial density of wild edible oyster mushroom. The mushroom samples were pretreated by steeping in 0.5% citric and sodium metabisulphite at room temperature for 10 minutes before being subjected to sun and cabinet drying until a constant weight was reached. The dried samples including the control samples (Samples not pretreated with chemicals) were evaluated for proximate, mineral composition and microbial density. The proximate analysis (protein, ash, fat, moisture and fibre) showed that untreated mushroom samples (both sun and cabinet dried) had the overall best results followed by samples pretreated with 0.5% sodium metabisulphite while samples pretreated with 0.5% citric acid had the lowest values. The mineral analysis (calcium, sodium, magnesium and potassium) of the mushroom samples followed the same trend as the proximate analysis. The microbial density of the samples showed that samples pretreated with 0.5% citric acid had the lowest count followed by samples pretreated with 0.5% sodium metabisulphite while the untreated samples had the highest microbial density. This implies that pretreatment with citric acid and sodium metabisulphite reduced the microbial density which may invariably extend the storage life of the edible oyster mushroom.

Pretreatments and drying are commonly used before drying tomatoes to inactivate enzymes, improve the drying process, and improve the quality of dried tomato powders. In this review, the effects of different pretreatments (osmotic solutions), dehydration methods, and packaging materials on the quality attributes of tomato powder were summarized. These include pretreatments and osmotic agent solutions (potassium metabisulfite, calcium chloride, sodium metabisulphite, ascorbic acid, citric acid, sodium chloride, and sodium benzoate), thermal blanching (steam blanching and hot water) and non-thermal-processes-like-freezing, sulfuring, etc. and drying methods (oven, sun, and indirect solar dryer). The tomato powders were dried to preserve, store, and transport them. Drying implies not only physical changes, which the consumer can easily detect through visual inspection but also chemical modifications. These are responsible for alterations in color, flavor, and nutritional value, which compromise the overall quality of the final tomato powder. Maximum lycopene, vitamin A, and C contents were found in freeze-dried and direct sundried than samples dried using other methods at low drying temperatures. Freeze driers showed in keeping the nutritional quality of tomato powder with a combination of different pretreatments. Different pretreatments including osmotic agent solutions have their own merits and demerits for the final tomato powder. To overcome the drawbacks of nutritional quality, non-thermal pretreatment categories may be a better alternative to thermal blanching, and more fundamental research is required for better design and scale-up.