Freezing and thawing are heat transfer processes, involving chemical changes which may greatly affect product quality. Due to sparse literature on freeze-thawed cycles and its effects on soups quality, the effect of freeze-thaw cycles on the nutritional quality of selected Nigerian soups has to be investigated. Soups (Ila, Ewedu, Ogbono, and Kuka) were prepared using standard recipes. The soups were packaged in plastic and aluminum containers, frozen at -20°C, and thawed with microwave oven, hot water (100°C), and at ambient condition for four cycles of 5-day interval. After each cycle, chemical compositions of the samples were determined using AOAC methods. Data were analyzed using ANOVA at P = 0.05. Moisture, protein, fat, crude fiber, ash, and carbohydrate contents of the freeze-thawed soups were 63.6-88.6%, 3.6-8.8%, 1.0-6.1%, 0.8-1.2%, 1.8-4.6%, and 0.9-15.6%, respectively. Mineral contents were iron (5.0-6.8 mg/100 g), calcium (68.1-190.8 mg/100 g), sodium (144.4-231.7 mg/100 g), potassium (200.4-302.1 mg/100 g), and phosphorus (228.0-337.2 mg/100 g). Vitamins were vitamin A (29.5-59.9 mg/100 g), vitamin B (10.1-36.4 mg/100 g), and vitamin E (28.4-90.2 mg/100 g). Microwave-thawed plastic soups had limited nutritional losses when compared with other thawing methods, and should not be extended beyond the third cycle because of increasing reduction in fat and protein, indicating deterioration.
Keywords: Freezing; nutritional quality; soups; thawing.