Abstract: The effects of four freezing methods on the quality of baked sweet potatoes were studied. The baked sweet potatoes were treated by -18 ℃, -25 ℃, -60 ℃ refrigerator freezing and liquid nitrogen quick-freezing, respectively. The changes of physical and chemical indicators, including starch, fat, reducing sugar, ascorbic acid, carotene, L*, hardness, chewiness and maximum shearing force, were analyzed, and the freezing curves were described. Correlation analysis and principal component analysis were used to evaluate the nutritional quality of the baked sweet potatoes under different freezing rates. Results showed that the time of liquid nitrogen through the maximum ice-crystal formation zone was shortest, and its texture characteristics were closest to fresh-baked sweet potatoes. The preservation for major quality parameters and color was best after freezing at -60 ℃ compared with other freezing methods. Correlation analysis approved that there was a certain correlation among most quality indexes, and the influence of chewiness on the baked sweet potatoes quality was greatest. Principal component analysis indicated that 11 quality characteristics were consolidated into three principal components, and the cumulative variance contribution rate was 93.94%, which reflected the most information of baked sweet potatoes. Protein, chewiness, elasticity and reducing sugar and carotene were selected as the core indexes to evaluate the comprehensive quality of baked sweet potatoes. In a word, -60 ℃ refrigerator freezing is beneficial to maintain the nutritional quality of pre-frozen baked sweet potatoes. The present study provides data support for the comprehensive evaluation and further research and production of pre-frozen roasted sweet potatoes.
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