89B-33 |
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M. DAVENPORT, H. G. Kristinsson, and H. Q. Nguyen. Dept. of Food Science & Human Nutrition, Univ. of Florida, 130-B Aquatic Foods Pilot Plant, PO Box 110370, Gainesville, FL 32611-0370 The use of acid and alkali-aided processing to isolate fish protein with good functional properties is a recent technique. The quality of the raw material and different processing pH values may affect the recovery of the proteins and their gel forming ability and thus the economic viability of these processes. The objective was to study if fresh, aged and frozen raw material would affect the recovery and gelation properties of PIs extracted with the acid and alkali-aided processes. Catfish muscle was ground and either (a) immediately isolated, (b) kept at 4° C for 7 d. and isolated, and (c) frozen for 7 d. at -25° C and isolated. Protein homogenates (1:6 dilution) were adjusted to low (2.5) and high pH (11.0) and centrifuged at 10,000g. Recovered soluble proteins were then readjusted to 5.5 and centrifuged at 10,000g to recover the PIs. Gel formation of the PIs was investigated at 20% protein using a rheometer and oscillatory testing. Protein recovery was calculated. Protein recovery was slightly higher for the acid-aided process. Frozen raw material led to reduced recovery. Alkali-aided processing gave PI with significantly better gel forming ability than the acid process for fresh and aged raw materials. The state of the raw material affected gel strength in the following order (strongest to weakest gels): fresh>aged>frozen. The gel forming ability of the previously frozen raw material was poor for both isolates. The very similar low gel strength after freezing for both the acid and alkali PI may indicate that freezing modified protein structure to a greater extent than the isolation conditions. This study showed that different pretreatments of raw materials, especially freezing, can have markedly different effect on the properties of isolated catfish proteins. More research is underway to understand the molecular mechanisms behind this difference.
Session 89B, Aquatic Food Products: Surimi, gels and by-products
2005 IFT Annual Meeting, July 15-20 - New Orleans, Louisiana |