Effects of Multiple Freeze-Thaw Cycles on Biochemical and Physical Quality Changes of White Shrimp (Penaeus vannamei) Treated with Lysine and Sodium Bicarbonate.

Freezing and thawing occur during storage, transportation, and retail display, leading to deterioration of frozen shrimp. The objective of this research was to investigate the change in quality of frozen white shrimp treated by lysine and NaHCO3 after multiple freeze-thaw cycles. Shrimp were soaked in lysine and lysine/NaHCO3 each at 1% (w/v) frozen in an air-blast freezer at -30 °C, and kept in a chest freezer (-18 ± 2 °C) for a week before they were thawed using tap water before the analysis (freeze-thaw cycle 1). The samples were subjected to five freeze-thaw cycles, which were repeated every week. Qualities of the samples were determined for thawing loss, cutting force, and total volatile basic nitrogen (TVB-N), as well as oxidation stability by using Rancimat. The use of lysine/NaHCO3 could significantly reduce thawing loss at all freeze-thaw cycles compared to the control and lysine treatment (P < 0.05). Similar results were found with TVB-N and the oxidation stability of the samples. A difference in cutting forces of the shrimp between lysine and lysine/NaHCO3 treatment was found when the frequency of freeze-thawing was increased to three cycles; it was lower than that in the control at all cycles. Histological study showed that the treatment with lysine/NaHCO3 led to the swelling of muscle fibers and fewer fragments at five freeze-thaw cycles. The results showed that lysine/NaHCO3 could effectively retard the quality loss from repeated freeze-thawing during frozen storage. PRACTICAL APPLICATION: Repeated freezing and thawing usually occur during storage, transportation, retail display or in restaurants, and in consumers' kitchens. The temperature at the manufacturing site and during transportation in a tropical country like Thailand is relatively high, and frozen food producers come across quality deterioration resulting from multiple freeze-thaw cycles occurring during transportation and storage. Frozen shrimp producers require research to improve product quality by adding nonphosphate food additives or, if possible, by using natural food ingredients instead of polyphosphate or sodium bicarbonate.

Physicochemical Properties of Defatted Rambutan (Nephelium lappaceum) Seed Flour after Alkaline Treatment.

Rambutan seeds were subjected to SC-CO2 extraction at 35 MPa, 45 °C to obtain defatted rambutan seed flour. Its physicochemical properties before and after treatment with alkali solution using 0.075 N NaOH were investigated. Alkali-treated flour had a significant increment in bulk density, swelling power, water adsorption capacity, emulsion capacity and stability but a reduction in turbidity, solubility and oil absorption capacity. Pasting measurements showed peak viscosity, breakdown, setback and final viscosity increased significantly for the alkali-treated flour, while pasting temperature decreased. The alkaline treatment decreased the least gelation concentration, but increased the apparent viscosity.

Expansion and functional properties of extruded snacks enriched with nutrition sources from food processing by-products.

Rich sources of protein and dietary fiber from food processing by-products, defatted soybean meal, germinated brown rice meal, and mango peel fiber, were added to corn grit at 20 % (w/w) to produce fortified extruded snacks. Increase of total dietary fiber from 4.82 % (wb) to 5.92-17.80 % (wb) and protein from 5.03 % (wb) to 5.46-13.34 % were observed. The product indicated high expansion and good acceptance tested by sensory panels. There were 22.33-33.53 and 5.30-11.53 fold increase in the phenolics and antioxidant activity in the enriched snack products. The effects of feed moisture content, screw speed, and barrel temperature on expansion and nutritional properties of the extruded products were investigated by using response surface methodology. Regression equations describing the effect of each variable on the product responses were obtained. The snacks extruded with feed moisture 13-15 % (wb) and extrusion temperature at 160-180 °C indicated the products with high preference in terms of expansion ratio between insoluble dietary fiber and soluble dietary fiber balance. The results showed that the by-products could be successfully used for nutritional supplemented expanded snacks.

Characteristics and antioxidant of Ulva intestinalis sulphated polysaccharides extracted with different solvents.

Ulva intestinalis, a tubular green seaweed, is a rich source of nutrient, especially sulphated polysaccharides. Sulphated polysaccharides from U. intestinalis were extracted with distilled water, 0.1N HCl, and 0.1N NaOH at 80°C for 1, 3, 6, 12, and 24h to study the effect of the extraction solvent and time on their chemical composition and antioxidant activity. Different types of solvents and extraction time had a significant influence on the chemical characteristics and antioxidant activity (p<0.05). Monosaccharide composition and FT-IR spectra analyses revealed that sulphated polysaccharides from all solvent extractions have a typical sugar backbone (glucose, rhamnose, and sulphate attached at C-2 or C-3 of rhamnose). Sulphated polysaccharides extracted with acid exhibited greater antioxidant activity than did those extracted with distilled water and alkali. The results indicated that solvent extraction could be an efficacious method for enhancing antioxidant activity by distinct molecular weight and chemical characteristic of sulphated polysaccharides.