Effects of Freeze-Thawing and Dehydration of High-Moisture Unutilized Raw Materials on Water Removal, Nutrient Values and Dry Matter and Crude Protein Digestibility Using an <i>In Vitro</i> Method in Pig

<p>The effect of freeze-thawing and dehydration on water removal and nutrient changes in high-moisture unutilized raw materials and digestibility were investigated using artificial digestion experiments. In this study, the cut lower portions of asparagus stalks, non-standard potatoes and waste tofu were used as typical unutilized raw materials with a high water content. Four treatments were studied: a control treatment - using the raw materials as received; a dehydration treatment - using a dehydrator; a freeze-thawing treatment - thawing after freezing; and a freeze-thawing dehydration treatment - dehydrating after freezing and thawing. For asparagus, the moisture content and rate of moisture removal after the control (raw materials) and dehydration treatments were not significantly different, but after the freeze-thawing and freeze-thawing dehydration treatments, the moisture content was lower and the rate of moisture removal was higher compared with the control (raw materials) and dehydration treatments. In contrast, the moisture content of the potato and tofu was lowest after the freeze-thawing dehydration treatment, followed in increasing order by the freeze-thawing, dehydration and control (raw materials) treatments, with the rate of moisture removal from highest to lowest being in reverse order. The times required for drying in the freeze-thawing and freeze-thawing dehydration treatments were approximately half those required for the control (raw materials) and dehydration treatments. The contents of crude protein and crude ash in the asparagus and potato decreased in the order of control (raw materials), dehydration, freeze-thawing and freeze-thawing dehydration treatments, with the contents of carbohydrate increasing in both asparagus and potato. The crude fat content of asparagus increased in the order of the control (raw materials), dehydration, freeze-thawing and freeze-thawing dehydration treatments, and decreased in potato. There was no difference in the nutrient contents of tofu between the four treatments. There was no difference in digestibility of crude protein measured by the artificial digestion experiments between asparagus, potato and tofu. The dry matter digestibility of asparagus and potato after the freeze-thawing and freeze-thawing dehydration treatments was lower than that after the control (raw materials) and dehydration treatments. The dry matter digestibility of asparagus and potato after the freeze-thawing and freeze-thawing dehydration treatments was lower than that after the control (raw materials) and dehydration treatments, but there was no difference in tofu between the four treatments. These results suggest that freeze-thawing or freeze-thawing dehydration treatments effectively removed water from the raw materials thus shortening their drying times, although these treatments affected the nutrient content and dry matter digestibility.</p>