Effect of freezing temperature on molecular structure and functional properties of gelatin extracted by microwave-freezing-thawing coupling method

The effect of different freezing temperature (-20 degrees C, -40 degrees C and -80 degrees C) on the properties (mainly molecular structure and functional properties) of gelatin extracted by microwave-freezing-thawing coupling method were compared systematically. The results showed that as the decrease of freezing temperature (-20 degrees C similar to -40 degrees C), the yield and gel strength increased from 11.80% to 14.55% and 753.00 g-825.67 g respectively due to the easier dissolution of subunit components induced by destruction of fish skin structure, while the lower freezing temperature (-80 degrees C) resulted in decrease of gel strength (734.00 g) due to the easier degradation of subunit components induced by excessive destruction of fish skin structure during the microwave extraction process. The FTIR results confirmed the destruction of the triple helix structure of gelatin at freezing temperature -80 degrees C, thus decreasing the thermal stability and exposing more hydrophilic amino acids with a reduced surface hydrophobicity (281.72-200.21). At freezing temperature (-40 degrees C), the gelatin showed the best foaming property and emulsifying properties, attributing to the lower interface tension induced by higher hydrophobicity. This study would provide guiding significance for the industrial production and the regulation of the physicochemical and functional properties of green gelatin.