Study On The Preparation Of Clean Label Starch By Dry Heat Treatment And Its Application In Yogurt

Yogurt is a kind of dairy product with high nutritional value and special flavor,which is favored by consumers due to its unique flavor,improving intestinal health and promoting intestinal absorption.During the processing of yogurt,thickening stabilizers such as chemical cross-linked starch are usually added to maintain the stability of systems to prevent low viscosity,rough texture,poor taste,and whey precipitation during storage.However,chemical modification is less desirable in food applications.Besides,with the improvement of consumers' awareness of food additive labels,yogurt with clean labels has become the first choice of consumers.Therefore,the key to solve the problem is to develop and design a kind of starch that has the characteristics of clean label and meets the functional requirements of yogurt thickening stabilizer.In this paper,waxy corn starch was selected as the raw materials and modified by dry heat treatment.Taking the heat resistance stability as the inspection index,the technological parameters of dry heat treatment for preparing clean label starch were determined and optimized.Then,the effect of dry heat treatment conditions on multi-scale structures and physicochemical properties of starch was studied.Additionally,the mechanism of dry heat treatment regulating the heat resistance of starch was explored.The application of clean label starch in stirred yogurt products was realized.The main research contents of this paper were as follows:Firstly,the effect of dry heat treatment on pasting properties of waxy corn starch was examined.After determining the gelatinization characteristics of the thickening stabilizer for yogurt,the influence of different p H,reaction temperature and time on thermal stability of starch was explored.The results showed that the starch prepared under the conditions of p H 9,reaction temperature 160°C and reaction time 3 h had the best heat-resistance stability.The breakdown value of the starch reduced from 925 m Pa·s to 6 m Pa·s,final viscosity increased by 98.0%.The stability test showed that the sample had the same level of heat resistance,acid resistance and shear stability as esterified and etherified cross-linked starch,and it was suitable for use as a thickening stabilizer in the yogurt systems.Secondly,the influence of dry heat treatment on multi-scale structures of waxy corn starch such as granule morphology,crystal structure,spiral structure and layered structure,was systematically explored,and mechanism of heat resistance,acid resistance and shear stability was explained using a variety of modern analytical instruments.The results showed that dry heat treatment caused the surface of starch granules to shrink,and the granular shape remained intact under an optical microscope after high-temperature gelatinization;the molecular chain was degraded and the double helix structure was untwisted;the relative crystallinity and molecular weight were reduced;The amylose content of the native starch increased from 3.71% to 7.56%.The heat energy in the dry heat treatment system,on the one hand,led to the destruction of multi-scale structure of waxy corn starch to varying degrees,resulting in the decrease of gelatinization temperature and enthalpy,in which the gelatinization enthalpy decreased by 2.58?4.77 J/g.On the other hand,the free movement of waxy corn starch molecular chain after degradation was enhanced,and rearrangement and orientation were more likely to occur.During dry heat treatment at a higher temperature,the relative content of double helix structure and amorphous region decreased,in which the content of amorphous region decreased by 3.64%;the thickness of semi-crystalline layered structure increased,and ordered degrees of starch aggregate structure and crystalline region of the layered structure had increased.These multi-scale structural changes promoted the heat-resistant stability of starch molecules in varying degrees,giving them unique gelatinization properties.Finally,the stirred yogurt was prepared with clean label starch as raw materials,and the application feasibility of clean label starch in yogurt was explored by investigating the morphology of starch in stirred yogurt and the storage stability,rheological properties and sensory evaluation of yogurt.The results showed that the clean label starch preserved a large number of complete starch granules in yogurt products,promoting the formation of a dense and uniform gel network structure.The water holding capacity of yogurt with clean label starch was better than that of yogurt with native starch during low-temperature storage within21 days.The water holding capacity of yogurt with clean label starch increased by 18.80% on the 21 st day compared with the native starch group,and was better than chemical cross-linked starch group(10.93%).The apparent viscosity and rheological properties of yogurt with clean label starch were also better than those of yogurt with native starch group,which was similar to the application effect of chemically cross-linked starch.The results of sensory evaluation showed that the stirred yogurt with clean label starch had the best comprehensive sensory properties and the highest acceptability.It could be seen that the clean label starch prepared in this paper had a good application effect in stirred yogurt,and it was a better choice for thickening stabilizers in yogurt.