Technology of physically modification of potato starch and their applications in food products

Abstract

The thesis is dedicated to the development of the technology of modified potato starch by using physically modification of heat-moisture treatment (HMT) combined with microwave treatment (MW), and thesis is dedicated to the scientific substantiation development of the technology of food products with incorporation of modified potato starch. This first section of this thesis presents the results of an analytical review of literary sources, namely, the relationships between the properties and structure of starch, the analysis of physical, chemical and enzymatic modification of starch, and the application of modified starch in food. HMT and MW are the most appealing physical modification method of starch due to their advantages of environmental protection, no reagent by-product, easy control process and safe for industrial pro-duction. Therefore, the literature review especially focuses on the effects of HMT and MW on the properties of starch. On the basis of analyzing the literature, the scientific problem of this thesis is expounded in the second section, the choice of objects and the direction of researches is substantiated, methods of fundamental and applied researches are resulted. In accordance with the objectives of the study, a work program was formulated, which not only provides the studies of modification technological processes of single heat-moisture treatment of native potato starch to determine the optimal parameters and the studies of modification technological processes of heat-moisture treatment combined with microwave pre- and post-treatment, but also provides the determination methods of physicochemical properties of starch paste, physicochemical properties of starch granules, multiscale structure of starch granules, and provides the potential application of heat-moisture treatment and microwave treatment modified potato starch in food products (cookies, fresh noodles and steamed bread). In order to achieve the established tasks, the research methods and techniques are demonstrated and their descriptions are given. The third section of this thesis systematicall studies the effects of HMT conditions the morphological, physicochemical and in vitro digestion properties of potato starch and its process optimization presented a comprehensive understanding of the effects of HMT conditions on functional and digestibility properties of starch, as well as the related mechanism, which would provide a useful theoretical basis for further studies on improving the application of thermal treatment technology in starch modification. The transparency and retrogradation stability of potato starch after HMT were reduced, solubility and swelling power varied with the gelatinization temperature. HMT can significantly affect the textural properties of potato starch and the hardness, gumminess, chewiness and resilience of HMT starch gels first increased significantly and then decreased with the extension of treatment time. Short heating time (<1.5 h), relatively low heating temperature (<100°C) and low moisture content (<25%) of HMT process can significantly enhance the texture properties of HMT starch gels. The HMT potato starch pasting properties results indicated that it is necessary to select appropriate heat-moisture treatment conditions for the preparation of vermicelli food by using the HMT potato starch in order to obtain better edible quality. HMT had great effect on the particle size, morphological, structural, and digestive properties of potato starch. HMT led to large particle size, rough surface of starch granules and resulted in hollow structure located at the hilum of potato starch granules. XRD results showed an increased relative crystallinity and transformed crystalline structure from B-type to C-type with the extension heat moisture treatment. FTIR spectroscopy results indicated that the heat moisture treatment may result in the breaking of starch molecular chain or the breaking of the associative hydrogen bond of starch molecule. In vitro digestion results showed that HMT process could significantly decrease rapidly digested starch (RDS) content, but increase resistant starch (RS) content, which indicating HMT starches could potentially become sources of industrial-resistant starch and as low-calorie food ingredients. The optimized process parameters of setback viscosity of HMT were as follow: the temperature was 90°C, the time was 1.5 h and the moisture content was 23.56%. Under such conditions the maximum theoretical setback viscosity value was 3871 cP. The verification experiment showed the actual mean setback viscosity was 3677 cP and there was little error between the actual setback viscosity and theoretical setback viscosity. Compared with native potato starch (NS), optimized heat-moisture treatment modified starch (HMTS) had lower peak viscosity (2966 cP), lower hold viscosity (2882 cP) and lower breakdown viscosity (84.5 cP), but higher paste temperature (71.1°C), higher final viscosity (6559 cP) and setback viscosity (3677 cP). The hardness, cohesiveness, gumminess, chewiness of NS gel were 2706 g, 0.63, 1700 g, 1404 g·mm, respectively, while the hardness, cohesiveness, gumminess, chewiness of HMTS gel were 6082 g, 0.73, 4920 g, 3570 g·mm, respectively. Compared with the NS gel, the hardness, cohesiveness, gumminess and chewiness of HMTS gel were increased significantly, and there was no significant difference in springiness and resilience. The retrogradation of NS and HMTS increased with the extension of storage time, and the HMTS had higher retrogradation than that of NS, indicating that potato starch modified by heat-moisture treatment was more prone to retrogradation. In vitro digestion results showed that HMTS had higher slowly digested starch (SDS) content and RS content than that of NS, but lower RDS content. Compared to the native potato starch, the RDS decreased by 10.05%, the SDS increased by 5.06% and the RS increased by 2.48%, respectively in the optimized HMT potato starch. The effects of HMT assisted by MW pre- and post-treatment on the morpho-logical, physicochemical and in vitro digestion properties of potato starch were also evaluated in the fourth section of this thesis. This research presented a comprehen-sive understanding of the effects of HMT and MW bi-directional modifications on functional and digestibility properties of starch, as well as the related mechanism, which would provide a useful theoretical basis for further studies on improving the application of microwave technology in starch modification. All the starch samples modified by single HMT, single MW, and dual modifi-cation of HMT combined with MW showed lower swelling power than that of na-tive starch when the test temperature was 65–85°C, while opposite results were ob-tained at 95°C. All the modified starch samples showed higher solubility than that of native starch when test temperature was 75–95°C. Single MW, short-time single HMT and short-time HMT combined with MW pretreatment can enhance the re-peated freeze-thaw stability of potato starch pastes, while long- time HMT ( 4h) could weaken the freeze-thaw stability of potato starch. Dual modification of HMT and MW had greater effects on starch retrogradation than that of single HMT or single MW, moreover, HMT combined with MW pretreatment also had greater ef-fects on starch retrogradation than that HMT combined with MW post-treatment. HMT heating time had great significant effect on starch paste transparency, dual modification of HMT combined with MW had greater effect on the transparency of starch paste than that of single HMT and MW. The hardness, cohesiveness, gummi-ness and chewiness of all the HMT modified potato starch gel (including single HMT, HMT combined with MW) decreased with the extension of heating time. The HMT potato starch pretreated by MW had higher hardness value than that of HMT potato starch post-treated by MW. HMT treatment caused a slight increase of lightness (L* values), while single MW treatment caused a slight decrease of lightness, indicating that the color of all the HMT treated samples (HMT, MW-HMT, HMT-MW) became brighter and the color of the single MW treated sample (MWS) became darker. The starch particle size distribution experiments showed that D50, D (4,3) and D (3,2) of all treated starch were higher than NS, while the value of S.S.A. was significantly decreased by MW and HMT, indicating that MW and HMT treatments can caused expansion, partial gelatinization and agglomeration of starch granules, resulting in large parti-cle size of starch granules, which were consistent with the results of scanning elec-tron microscopy (SEM). The results of water distribution in potato starch showed that he bound water in all starch samples was the main water which at least ac-counted for 90%, the MW treated starch had three different state water, while NS and single HMT treated starch only had two different state water. There were signif-icant differences of PT21 and PT22 between NS and all treated starch, NS had the lowest PT21 but highest PT22, indicating that MW and HMT treatments could change the water distribution and improve the interaction between starch and water. Dual starch modification via MW and HMT made the surface of starch gran-ules rougher and caused more serious depressions or scallops than single modifica-tion with MW or HMT, especially in the case of HMT-MW, which can be verified from the scanning electron microscopy, normal light and polarized light microsco-py that some depressions or potholes appeared on the surface of starch granules af-ter modification, and the center of polarized cross structure slowly expanded. All the treatments increased the pasting temperature and setback viscosity but de-creased peak viscosity and breakdown viscosity of starch. The FT-IR and XRD spectra implied that HMT and MW destroyed the double helices and crystalline structure of potato starch. All treatments increased the content of RS but reduced the content RDS of potato starch. Under the same HMT heating duration, the RS content of starch modified by HMT combined by with MW post-treatment was sig-nificantly higher than that of starch modified by HMT combined by MW pre-treatment and single HMT. The information obtained in this research might be ben-eficial to the industrial applications of microwave and heat-moisture techniques de-ployed to modify starch and eventually produce new starch materials satisfying the potential consumer requirements. The fifth section of this thesis also presents the results of the effects of substi-tution of wheat flour with potato starch modified by heat-moisture treatment and microwave treatment on the quality characteristics of three typical food products including cookies, fresh noodles and steamed bread, which would provide a benefi-cial theoretical basis for further research on the application of HMT and MW modi-fied starch in food. In this research the HMT modified potato starches (HMTS) were prepared by HMT at 90°C for 1.5 h with 23.56% moisture content of starch (the optimized process parameters of HMT), whereas the MW modified potato starches (MWS) were prepared by MW at 400 W power for 5 min with 25% mois-ture content of starch. The substitution of low protein flour (the protein content was 7.0%±1.5%) with HMTS or MWS in quantity above 5% made cookies brighter, yellower, and less reddish. The differences in color between the control and experimental cookies were detectable by the human eye when the substitution amount of low protein flour with HMTS or MWS reached 5%.The hardness (included average hardness, surface hardness and max hardness) of cookies with HMTS or MWS was signifi-cantly lower than of control (P value <0.05), but higher crispy value, indicating less work to be consumed when chewing. The addition of appropriate amount of HMTS or MWS to cookies could improve the appearance. Cookies with addition of HMTS or MWS powder in the amount of 15% not only had crispy taste, but also had the highest acceptability score and yellowest color, therefore, the appropriate incorpora-tion of HMTS or MWS was 15%. The present research might help to enlarge the application of modified potato starch in confectionery products. Substitution of with HMTS or MWS altered the texture and tensile properties of dough. Through correlation analysis, it has been concluded that the dough tensile properties of resistance to extension and extensibility were extremely significant positive correlated with the cooked fresh noodles tensile properties of tensile strength and elasticity. Substitution wheat flour (the protein content was 10.0%±1.0%) with HMT and MW modified potato starch (HMTS and MWS) significantly decreased the optimal cooking time of fresh noodles (P value< 0.05), the dry matter water absorption rate and loss rate of dry matter significantly increased with the in-crease of substitution amount of HMTS and MWS. When the incorporation amount of HMTS was less than 30% and the incorporation amount of MWS was less than 20%, the noodles could maintain good organoleptic and cooking quality attributes. More than 30% of HMTS or 20% MWS will deform the noodles and cause break-age. Therefore, the maximum incorporation of HMTS or MWS should be 30%, 20%, respectively. The present research results can be applied to the noodle industry, and it might also help to enlarge the application of modified potato starch in cook-ing noodle-like food. The appropriated amount of substitution of wheat flour (the protein content was 10.0%±1.0%) with HMTS or MWS not only can maintain the quality of steamed bread, but also increase the nutrition of steamed bread. The specific vol-ume of steamed bread decreased with more incorporation of HMTS or MWS. The specific volume of steamed bread buns made by incorporating MWS was lower than that of steamed bread made by incorporating HMTS, which indicated that MWS had greater impact on the specific volume of steamed bread than HMTS. The experimental steamed bread showed higher L* and a*, but lower b* values than those of the control steamed bread, and the color changes was more obvious with the increase of substitution level of HMTS or MWS, indicating that steamed bread with more incorporation of HMTS or MWS displays lighter transparent color. When the substitution level of HMTS or MWS was higher than 30%, 20%, respec-tively, the differences in color (ΔE>3) between the control and experimental steamed bread can be detectable by the human eye. Texture properties of steamed bread were affected with substitution due to the disruption of dough structure, and the incorporation of HMTS or MWS led to higher value of hardness, gumminess and chewiness, whereas the value of springiness, cohesiveness and resilience were reduced, which indicated that the incorporation of HMTS or MWS led to firmer and denser structure of steamed bread. The sensory total scores decreased with more incorporation of HMTS or MWS. The total sensory score of was higher than 80 when the substitution level of wheat flour with HMTS or MWS was less than 30%, indicating the produced CSB can be accepted by consumers. Based on the above research results of steamed bread quality, the optimal substitution of wheat flour with HMTS or MWS was 30%. Moreover, the results of postprandial blood glucose levels of participants at different times after eating steamed breads indicated that products prepared with incorporation of HMTS or MWS were more suitable for di-abetics or the elderly. This research can provide valuable guidance for further application of HMT and MW modified potato starch in wheat-based products, and it is also of great sig-nificance for promoting potato as staple food.