Effects of freezing-thawing pretreatment combined with liquid nitrogen and dilute acid on the gelatinization of collagen

The method of liquid nitrogen quick-freezing combined with dilute acid rapid-thawing was applied as a pretreatment to extract gelatins from pigskins, and the influence of HCl concentration (0-2% (v/v)) on the gelatinization of collagen in pigskins was observed. The freezing-thawing using liquid nitrogen and water did not effectively induce the gelatinization of collagen, and the replacement of water with dilute HCl solutions improved this situation. The gelatin pretreated with liquid nitrogen and 1% HCl showed the highest yield and strongest gel properties, since the hydrogen bonds balance and the triple-helical structure in collagen were damaged moderately after this pretreatment to promote the release of subunit components in collagen during gelatin extraction. The surface of the gelatinized collagen via freezing-thawing pretreatment with liquid nitrogen and 1% HCl showed a similar honeycomb shape as traditional acid pretreatment. However, the pretreatment time could be shortened from 6 h (traditional acid method) to 20 min. Therefore, the freezing-thawing method combined with liquid nitrogen and dilute acid could be potentially used in gelatin preparation.