南极细菌胞外多糖溶液冻结特性的差示扫描量热研究

采用差示扫描量热法,测定几种南极细菌胞外多糖(简称,EPSs)溶液的结晶、熔融、焓转变以及水合性质等冻结特性,分析了EPSs的浓度和分子量与其抗冻活性的关系.结果表明,在溶液冻结过程中,仅0.25%的Pseudoalteromonas sp.S-15-13 EPSs(分子量,6.2×104Da)可抑制冰核形成,溶液冻结温度较纯水的降低(1.07±0.62)℃;溶液的冻结焓降低说明冰核生长变缓,冰晶形成细小,0.125%的Shewanella sp.5-1-11-4 EPSs(分子量,1.2×103Da)和Moritella sp.2-5-10-1 EPSs(分子量,3.0×103Da)冻结焓分别较纯水的降低17.15%和29.13%,S-15-13 EPSs在0.125%～0.5%的范围内可降低冻结焓,0.125%时冻结焓较纯水的低30%,其不冻水含量为(0.292 ±0.05) g/g.在冰晶熔化过程中,几种EPSs均可降低溶液熔融温度和熔融焓,促进冰晶熔化,使冰晶细小;4.0%的5-1-11-4 EPSs、2-5-10-1 EPSs和0.5% S-15-13 EPSs的熔融温度较纯水的分别降低(2.70±0.15)℃、(2.30±0.39)℃和(4.66±0.42)℃.研究结果阐明EPSs可以通过改变菌体周围水的冻结特性,以抵御冰晶对微生物的损伤,大分子量EPSs对冰晶的抑制作用强于低分子量的.

Freezing properties of Antarctic bacterial exopolysaccharides solutions by differential scanning calorimetry

The freezing, melting, enthalpy change and hydration properties of Antarctic bacterial exopolysaccharides (EPSs)solutions have been investigated by differential scanning calorimetry, and the possible relations between concentration, molecular weight and antifreezing activities of exopolysaccharides have also been analyzed. Experimental results showed that, during the course of freezing, only Pseudoalteromonas sp. S-15-13 EPSs (molecular weight, 6.2×10~4Da) at 0.25% could inhibit nucleation of ice, and depress the freezing temperature by (1.07±0.62)℃. Reduction of freezing enthalpies meant the inhibited growth of ice nuclei and reduced size of crystallites. As compared with pure water, Shewanella sp. 5-1-11-4 EPSs (molecular weight, 1.2×10~3Da) and Moritella sp. 2-5-10-1 EPSs (molecular weight, 3.0×10~3Da) at 0.125% could reduce freezing enthalpies by 17.15% and 29.13%, respectively. S-15-13 EPSs ranged between 0.125%-0.5% could reduce freezing enthalpies, EPSs at 0.125% could reduce freezing enthalpy by 30%, and its non-freezing water was (0.292±0.05) g/g. During the course of freezing, all the EPSs reduced the melting temperature and melting enthalpies, thereby enhanced the ice melting and reduced the size of crystallites. As compared with pure water, EPSs of 5-1-11-4 and 2-5-10-1 at 4.0%, EPSs of S-15-13 at 0.5% reduced the melting temperatures by (2.70±0.15)℃, (2.30±0.39)℃ and (4.66±0.42)℃, respectively. The results of this study suggested that, EPSs could change the freezing properties of ambient water to defense bacteria from the harm of ice. The anti-crystallites effect of EPSs was stronger with a higher molecular weight.