冻结-高压湿热解冻对多种淀粉中支链淀粉断裂的影响

冻结和高压湿热解冻是含淀粉面团在食品加工过程的必要工艺,在此过程中淀粉球破裂、部分支链淀粉断裂成为直链淀粉,给面团和食品的物理性状控制带来许多不可预见的结果。该文通过研究加热时间、加热温度、冷冻时间和解冻时间对糊化后的小麦、甘薯、马铃薯和玉米淀粉中直链淀粉含量的影响,间接反映支链淀粉断裂情况,结合冻结解冻前后淀粉分子量分布、链长分布、光学和电子显微镜图谱提出了冻结-解冻过程不同淀粉中支链淀粉可能断裂方式。结果表明,4种淀粉中的直链淀粉含量先升高后下降,直链淀粉含量在4种淀粉的中达到峰值的时间分别为48,48,48,72 h。光学显微照片观察表明,冻融处理会导致更多凝胶化淀粉球的破裂。对于小麦支链淀粉,冻融解冻过程支链淀粉中侧链长度为5、6、7个葡萄糖残基的侧链对应3种可能的断裂方式:2+2+1、2+2+2及2+2+2+1;对于甘薯支链淀粉,支链淀粉中侧链长度为10、11和13个葡萄糖残基的侧链对应3种可能的断裂方式:3+3+4、2+2+3+4及2+2+2+3+4;对于马铃薯支链淀粉,支链淀粉中侧链长度为5和6个葡萄糖残基的侧链对应3种可能的断裂方式:2+3、2+4、3+3;而玉米支链淀粉中,支链淀粉中侧链长度为7、8、9个葡萄糖残基的侧链对应3种可能的断裂方式:2+5,3+5,和3+3+3(其中1表示1个葡萄糖;2表示含2个葡萄糖的麦芽糖、3表示含3个葡萄糖的麦芽多糖、4表示含4个葡萄糖的麦芽多糖和5表示含5个葡萄糖的麦芽多糖)。该论文结果为培育具有冻融稳定性的淀粉种子提供一种全新的思路,即通过基因方法控制植物减少容易断裂淀粉侧链的合成。

Effects of unfreezing by autoclaving during freeze-thaw treatment on amylopectin breaking in different gelatinized starches

Abstract: Freezing and autoclaving-thawing were necessary steps to produce different food with starchy dough, in which the damage of starch granule and the rupture of some amylopectin into amylose brought many unpredictable effects to the physical properties of dough and food. Many studies had been carried out to hinder the detrimental effects of freeze-thaw treatment on food properties, but few of them were practical. The main reason was lack of the basic data about the property change of starch in dough during freeze-thaw treatment. Sweet potato, potato and maize starches were often added into dough to produce steam bread with a particular quality. The properties of those foods were traditionally controlled by empirical knowledge. It was difficult to investigate the effects of freezing-thawing treatment on properties of different starches when they were mixed together. So the starches were treated individually in the paper. The effects of heating temperature, heating time, freezing time and thawing time on change of amylose content in gelatinized wheat, sweet potato, potato and maize starches were determined, which indirectly reflected the fracture of amylopectin. The possible fracture modes of amylopectin in different starches during freezing-thawing process were presented based on analysis of the distribution of starch molecular weight, chain length distribution, optical and SEM micrographs before and after freeze-thaw treatment. The results showed that the amylose contents in all starches firstly increased and then decreased and the maximum amylose contents of those 4 starches were present when the freezing time was 48, 48, 48 and 72 h, respectively. So the freezing time of gelatinized wheat, sweet potato, potato and maize starches should not exceed 48, 48, 48 and 72 h, respectively. Light micrograph observations indicated that the freeze-thaw treatment made more gelatinized granules broken. There were 2 growths of amylose contents during freeze-thaw treatments, and the first was derived from amylose leaching of more broken granules and the second stemmed from fracture of amylopectin. For wheat starch, branched chains with 5, 6, 7 glucose residues were broke into 2+2+1, 2+2+2 and 2+2+2+1 residues respectively; for sweet potato starch, those chains with 10, 11, 13 glucose residues were broke into 3+3+4, 2+2+3+4 and 2+2+2+3+4 residues respectively; for potato starch, chains with 5, 6 glucose residues were broke into 2+3, 2+4 or 3+3 residues respectively; for maize starch, those with 7, 8, 9 glucose residues were broke into 2+5, 3+5 and 3+3+3 residues respectively. Freeze-thaw treatment made more amyloses leach out from granule, providing more amylose to involve in quick retrogradation, which led to the shortage of food shelf. Freeze-thaw treatment also could make amylose broken into polysaccharides and bring sweet taste to corresponding foods, which would deteriorate food properties. Those findings in the paper probably provided a way to screen seeds with freeze-thaw-stable starch. That is, genetic methods are used to control plants to reduce the synthesis of starch with side chains that are susceptible to breakage. Further studies in relation to interaction between those broken amyloses and proteins such as glutenin, gliadin should be performed deeply.