甘薯全粉加工中无硫复合护色工艺优化

摘要

为了优化甘薯全粉无硫复合护色工艺，该文通过考察柠檬酸、柠檬酸亚锡二钠、植酸、亚硫酸氢钠和抗坏血酸5种护色剂对甘薯全粉色泽的影响，优选出柠檬酸和抗坏血酸作为甘薯全粉加工合适的护色剂；通过正交试验，得到柠檬酸-抗坏血酸无硫复合护色剂的最佳护色工艺为：将10 mm厚的甘薯切片在质量分数为0.3%的柠檬酸和0.1%抗坏血酸的复合护色液中护色处理30 min，可使制得的甘薯全粉亮度值L*达90.58，多酚氧化酶的抑制率达88.13%。研究发现柠檬酸的添加能显著提高抗坏血酸的热稳定性；酶促褐变产物紫外-可见光谱扫描显示，加入复合护色剂后410 nm处吸收峰明显减弱，表明复合护色剂能有效抑制酶促褐变反应的发生；圆二色谱研究表明多酚氧化酶经复合护色剂处理后，酶蛋白二级结构中α-螺旋减少，而β-折叠结构增多，酶蛋白的分子构象被改变，从而降低多酚氧化酶活力。该文为甘薯全粉加工中的无硫复合护色工艺提供了参考。%Sweet potatoes are highly nutritious vegetables that are rich in calories and biologically active phytochemicals such asβ-carotene, polyphenols, ascorbic acid and dietary fiber. While the sweet potato is the seventh most important food crop grown in around 111 countries, China contributes about 80% of the world’s production of sweet potatoes, where the roots are used as food, animal feed and as a raw material for starch and noodle manufacture. Sweet potatoes are highly perishable and difficult to store. In developing countries, there are many problems related to storage and transportation of the raw sweet potatoes. Sweet potato flour is regarded as the ideal product to solve the storage and transportation problem which could expand its utilization in various areas of food production as well. But using sweet potato flour for product development is hindered by the discoloration from enzymatic browning. Using a color fixative is the most convenient and effective method , the commonly used color fixatives are Critic acid, Disodium stannous citrate,Phytic acid, Sodium sulfite , Ascorbic acid and so on. Among these chemicals, Sodium sulfite is the most effective one, but using Sodium sulfite could lead to SO2 residue which may threat human health seriously, earlier in 1986, the FDA had banned its use in fresh fruit and vegetables. Therefore we urgently need to develop a safe and efficient color fixative without sulfur to reach the purpose of improving the food taste, nutrition and safety. Because of its more comprehensive and efficient color protecting effect, compound color fixative was regarded as the feasible scheme to take the place of Sodium sulfite . In this paper ,Critic acid, Disodium stannous citrate,Phytic acid, Sodium sulfite and Ascorbic acid were selected as the color fixative to inspect their effects on the L*value of the sweet potato flour. Critic acid and ascorbic acid were selected as the preferred color fixative. Through regression orthogonal design, we confirmed that a better quality of sweet potato flour could be obtained through soaking the 10mm slices in the compound color fixative that contains a mass fraction of 0.3%critic acid and a mass fraction of 0.1%ascorbic acid for 30 min. At the same that the mass fraction was (0.4%), the L*value of the sweet potato flour treated with the compound color fixative could reach 90.58, which was similar with the product treated with Sodium sulfite, the polyphenol oxidase inhibition ratio could also reach 88.13%, higher than others treated with single color fixative. Finally, there was a preliminary exploration of the browning inhibition mechanism of the compound color fixative. The results showed that the addition of critic acid could enhance the thermal stability of ascorbic acid. The absorption peak of enzymatic browning products of polyphenol oxidase with a compound color fixative was significantly weakened at 410 nm in UV spectrophotometric, which indicated that compound color fixative could effectively inhibit the enzymatic browning reactions to reduce the formation of precipitation recognized as the browning products. Circular dichroism showed that the compound color fixative might reduce polyphenol oxidase activity by changing its molecular conformation. The amount ofα-helix in the secondary structure of polyphenol oxidase decreased as opposed to the increase ofβ-sheet. This study can provide references for the use of a compound color fixative without sulfur during sweet potato flour processing.