نشریه فرآوری و نگهداری مواد غذایی
پیاپی 4 (زمستان 1388)

Gelatin is polypeptide with high molecular weight which is derived from collagen of connective tissue, skin, bone and tendons. The most common source of gelatin in the world is skin and bone of cow and pig. However, spreading BSE and other related animal diseases made many consumers of these products concern about using related products. In this regard, fish gelatin has gained a lot of consideration as a valuable source of gelatin in comparison with cow skin and bone or other related wastes. One of the most important factors related to fish gelatin is its lower melting point in comparison with commercial source of gelatin. For this reason, it is useful for application in products which are used and served at cold temperature. In this study, amino acid composition of Phytophag's fish skin gelatin was determined. Also, the effects of different alkali and acid concentrations (0.05, 0.33, 1.025, 1.71 and 2 N) along with extraction temperature (45, 51, 65, 79 and 85 ˚C) on melting point and viscosity of Phytophag's fish skin gelatin were studied using CRCD with 5 levels and 4 replicates of central point. Results showed significant effects of different temperature and acid/alkali concentrations on viscosity, while no significant effects were observed for melting point.

Gelatin is widely used in foods as an important functional biopolymer. Yield of extraction and other quality parameters like gel strength vary according to pretreatment conditions. Also, these parameters are affected by source and type of collagen. In this project, the effects of different alkali and acid concentrations (0.05, 0.33, 1.025, 1.71 and 2 N) along with extraction temperature (45, 51, 65, 79 and 85 ˚C) on gel strength and extraction yield of Phytophag's fish skin gelatin were studied using CRCD which consists of 5 levels and 4 replicates of central point. The effect of different alkali concentration and temperature on yield of extraction was significant. However, different acid concentration and extraction temperature had no significant effect on yield. Mutual effects of alkali and acid concentrations showed significant effects on extraction yield but their effects on gel strength showed that by increase in alkali concentration, no changes observed in gel strength, while gel strength showed an increasing trend by increase in acid concentrations. The effects of different extraction temperature and acid/alkali concentrations on gel strength were significant.

The chemical characteristics and oxidative stability of virgin olive (VOO) and pumpkin seed (PSO) oils during heating at 180 °C were investigated. The oxidative stability was assessed by measuring the rate of changes in total polar compounds (TPC) content and polar fractions including triglyceride polymers (TGP), triglyceride dimers (TGD), oxidized triglycerides monomers (oxTGM), diglycerides (DG), and free fatty acids (FFA). The TPC compositions were analyzed by high-performance size-exclusion chromatography (HPSEC). The VOO had a higher level of oleic acid (62.17 vs. 38.42) while the PSO characterized by its higher level of linoleic acid (39.83 vs. 20.05). The VOO presented a higher ratio of unsaturated to saturated fatty acids than the PSO (5.37 vs. 4.17). The PSO showed significantly higher amounts of the FFA and peroxide value (0.39 % and 10.85 meq/kg, respectively) than the VOO (0.18 % and 6.89 meq/kg, respectively). The PSO contained a higher level of the antioxidative compounds including total tocopherols (725 vs. 585 mg/kg) and phenolics contents (66.27 vs. 25.67 mg/kg) than the VOO. Comparing the results of TPC contents and their compositions during the heating process indicated that the VOO underwent more degradation than the PSO.

Effects of different improving agent materials (water, oil, egg yolk, starch, glycerol, sorbitol and propylene glycol) on quality characteristics of Barbari flat bread fortified with soy flour were investigated. Initial moisture, water activity, width/height ratio and specific volume were evaluated immediate after baking. Hardness, crumb moisture and crust moisture were also estimated on 0,2,5,8 and 12th day. Results indicated that improving agent with water, starch, glycerol, and propylene glycol showed higher moisture content among the other samples. Bread with improving agent of oil and water had the least water activity and bread samples with improving agent of water had the highest specific volume. Width/height ratio was significantly difference for all the improving agent materials and water and starch improving agent had the least ratios. Hardness was increased by the time and the least initial hardness recorded for water, starch and propylene glycol but after 12 days the least hardness recorded for water, egg yolk, starch and propylene glycol improving agent. The highest crumb moisture was observed for water and starch improving agent while water improving agent and propylene glycol, glycerol and starch had the highest values for crust moisture. Organoleptice test indicated no significant difference among the improving agent materials excepted in shape and porosity in sorbitol and propylene glycol.

In this study yoghurt whey based fruit beverage was prepared by formulating a mixture of orange-tangerine juice concentrate, sugar, water and stabilizer with yoghurt whey (30-60%). The sensory evaluation was performed by 10 judges using 5-point hedonic scale to compare the flavor, consistency, color, smell, mouth feel and overall acceptability of the product. The orange-tangerine beverage with 30% yoghurt whey has the highest flavor, consistency, color, smell, mouth feel and overall acceptability scores. After ultra pasteurization and packaging in tetrapak pocket, the beverage was stored in room temperature and in refrigerator for 12 weeks. Data obtained from different measurements were statistically analyzed using Mstatc software with two factor randomized complete block design. Means of treatments were also compared using Dunckan multiple range test (P<0/01 & p<0/05). The results showed that there was a reduction in the flavor, smell, consistency, pH and overall acceptability scores but mouth feel characteristic had no significant decrease during the storage. The overall acceptability of the beverages was found to be fine at the end of the 12 week periods of storage in refrigerator and 10 week periods at room temperature.

Date fruit (Phoenix dactylifera L.) is consumable in the last three stages of development including Khalal, Rutab and Tamar. Normally, part of the matured date fruits are allowed to partially dry on the trees before they are harvested to enhance their reserve and storage quality. These fruits can be stored for long periods in the form of compressed packs but usually some part of fruits on the tree become dry, hard and unusable due to loss of much water. In current study, to find out best hydration conditions, the effects of 24, 48 and 72 hours hydration at 40 and 50°C on the moisture content, water activity, darkening, acidity and firmness of the dried Tamar fruit were studied. The results showed that among different hydration treatments which were applied to improve the quality of dried fruits, 48h hydration at 40°C and 24h at 50°C had the best effects on the fruit quality.

The changes in color (L, a, b and total colour difference, TCD) of canola oil (CAO) as affected by bene kernel oil (BKO, 0.05-0.4%) and its unsaponifiable matters (USM, 100 ppm) fraction during 48 h frying process at 180 ºC was compared with tert-butylhydroquinone (TBHQ, 100ppm) by the method of image processing. The BKO, TBHQ or USM were significantly capable of lowering the darkness (lowering L value), redness (increasing a value), yellowness (increasing b value), TCD, and total polar compounds (TPC) content of the CAO during the frying process. The effeciency of samples containing100 ppm USM and 0.1% BKO was the same as or much better than that of 100 ppm TBHQ. There was a strong correlation (R2=0.965) between the TPC content and TCD of the oils studied. Assuming that the maximum level of TPC content permitted in frying oils is 24%, the TCD of the oils studied should be ≤ 20.98.