| Proso millet(Panicum miliaceum L.)is an ancient crop and extensively cultivated in Russia,Ukraine,China,and India due to its short growth period and drought tolerance.The shelled proso millet called“Huangmi”and it is not only rich in nutrients but also can help prevent diabetes and cardiovascular problems.Therefore,it has received more and more attention,and related products have been continuously developed and promoted.According to the amylose content,proso millet can be divided into waxy(low amylose content)and non-waxy types(high amylose content).Due to the different quality characteristics,the waxy and non-waxy proso millet has great differences in the planting area and application direction.The appearance,nutrition and cooking and edibility qualities of proso millet have a significant impact on its production,processing and commercial characteristics.At present,most of the researches on proso millet have focused on stress resistance and crop cultivation.Studies on quality,especially cooking and eating quality,have rarely been reported.However,compared with main crops,the study of proso millet started late,and there are few reports on the quality of proso millet,which is in great contradiction with the growing consumer demand of proso millet.Firstly,the agronomic traits,yield shapes,and quality traits of waxy and non-waxy proso millet were compared.Then,five waxy and five non-waxy proso millet varieties were selected and the appearance,pasting properties,cooking and edibility,and in vitro digestibility of proso millet were studied.Next,the chemical composition,morphological properties,crystalline structure,ordered structure,thermal properties,and pasting properties of waxy and non-waxy proso millets during the cooking process were investigated.The study can find the regularity of the cooking process of waxy and non-waxy proso millet and reveal the reasons for the difference in cooking and eating quality of waxy and non-waxy proso millet.Finally,the starches of waxy and non-waxy proso millet were isolated and their structures and physicochemical properties were investigated.The objective of the studies about starch was to explain the differences in quality of waxy and non-waxy millet.In order to further expand the use of proso millet,the nutritional characteristics,active substances,physicochemical characteristics,and in vitro digestion characteristics of flours were evaluated,which can provide a theoretical basis for the development of proso millet sprout flour products and a new direction for the processing of proso millet.Main contributions of this work are as follows:(1)The core germplasm resources of proso millet showed rich genetic variation.There were some differences in agronomic,yield and quality traits of waxy and non-waxy proso millet cultivars,and the characteristics of cultivars of proso millets were relatively single.The core collections of proso millet had abundant variation and rich phenotypic traits and quality traits have large changes,which provides greater space for target plant type shaping and quality improvement.Each trait showed a significant correlation,and through its related traits,some traits can be quickly and effectively selected.The grain color of non-waxy proso millet varieties is mainly yellow,red and black;the grain color of waxy proso millet varieties is mainly red and white.The inflorescence color of waxy and non-waxy proso millet is mainly green,and the panicle type is mainly lateral.The yield of non-waxy proso millet cultivars was 3304.3-4515.3 kg/hm~2,with an average of 3987.9 kg/hm~2,and 86.4%of the yield was from 3500.0-4500.0 kg/hm~2.The yield of waxy proso millet cultivars was2750.7-3902.1 kg/hm~2,with an average of 3144.6 kg/hm~2,and 94.4%of the yield was lower than 3500.0 kg/hm~2.The content of yellow pigment in non-waxy proso millet cultivars varied greatly,while the content of yellow pigment in waxy proso millet cultivars varied slightly.The average protein content of waxy millet was 2.59%higher than that of non-waxy proso millet.At present,there is a single type of cultivated variety,which is far from meeting the diversified demands of production and market for proso millet varieties.(2)Waxy and non-waxy proso millet has significant differences in appearance and nutritional qualities.There were significant differences of physical properties(grain weight,length,and width)observed among the samples,but there were no significant differences within the species.The grain brightness(L*)of waxy proso millet is significantly higher than that of non-waxy proso millet,and the total color difference between waxy and non-waxy proso millet is significantly different.Non-waxy proso millet grains had a higher light transmittance and contained more horny-endosperm than waxy proso millet;however,waxy proso millet grains contained enough floury endosperm and had a typical opaque phenotype.The analysis of the nutritional quality of proso millet showed that proso millet was rich in fatty acids and amino acids,and rich in unsaturated fatty acids(86.5%-88.4%),which had high nutritional value.The results of Principal Component Analysis(PCA)showed that waxy and non-waxy proso millet was well separated in the fatty acid and amino acid score maps and aggregated into two types.(3)Waxy and non-waxy proso millet has significant differences in cooking edibility quality.The research on cooking characteristics of waxy and non-waxy millet found that non-waxy millet had lower soup p H and higher water absorption,volume expansion ratio,soluble solids,soup light absorption value and iodine blue value than those of waxy proso millet.The results indicated that the non-waxy proso millet is more suitable for making porridge because more components leached into the water caused the porridge will be thicker.Cooked non-waxy proso millet is hard whereas waxy proso millet is sticky.The Scanning electron microscope(SEM)results of the cooked proso millet grain well explained the reasons for the differences in the texture characteristics of the proso millet:compared with non-waxy proso millet,many branching structures that connected to form a network structure were observed in the cross sections of steamed waxy proso millet.The fast digesting starch in cooked non-waxy proso millet is significantly lower than that of cooked waxy proso millet,and its resistant starch content is significantly higher than that of cooked waxy proso millet,which showed that the starch in cooked non-waxy proso millet is more difficult to be digested.In addition,the slow digestible starch content in proso millet is high(47.56%-55.80%),which indicates that proso millet is an ideal food to provide energy.A total of 59 volatile substances(6 alcohols,14 aldehydes,22 alkanes,4 ketones,1benzenes,8 acid esters,2 amines,1 heterocycles and 1 olefins)were detected in the waxy and non-waxy proso millet congee.In the PCA of the total aroma components of the proso millet,the waxy and non-waxy proso millet gathered well.In addition,there is a certain correlation between the content of volatile substances and the amylose and fatty acid components.(4)During cooking,waxy proso millet grains are more easily gelatinized(Complete gelatinization time:waxy proso millet 20 min,non-waxy proso millet 25 min),but non-waxy proso millet is more deformed and less consistent.Starch granules in proso millet grains were gradually gelatinized from the outer region to the inner region with cooking time.After being completely gelatinized,the microstructure of waxy proso millet grains showed a branched structure,while that of non-waxy proso millet grains showed a honeycomb structure.The water absorption ratio,expansion ratio,soluble solid,and iodine blue value of cooked proso millets increased with the cooking time,and the water absorption ratio,soluble solid,and iodine blue value were more pronounced in non-waxy proso millets than in waxy proso millets.During the cooking process,the peak of amylose-lipid complex formation at20°2?continued to increase,eventually forming a typical V-shaped structure.During the cooking process,the order structure of starches were gradually destroyed,the enthalpy absorption peak gradually disappeared,the gelatinization viscosity of flour gradually decreased,and the reduction rate of waxy proso millet was higher than that of non-waxy proso millet.(5)Waxy and non-waxy proso millet starches have significant differences in structure and physicochemical characteristics.These differences are also one of the reasons for the difference in quality of waxy and non-waxy proso millet.The granules of waxy and non-waxy proso millet starches were presented the typical“Maltese cross”.The SEM showed that the starch granules of waxy andnon-waxy proso millet are regular polygons and spheres,and the particle size of proso millet is smaller.The crystallinity of non-waxy and waxy proso millet is 37.6%and 38.4%,respectively,which is higher than the crystallinity of several other coarse cereals.The waxy proso millet had a low setback value and showed good stability.Waxy proso millet starch had good stability and is suitable for use as a frozen food additive or food thickener;non-waxy proso millet starch had high retrogradation rates and are suitable for making vermicelli.(6)Germination is a simple and effective way to improve the nutritional and functional value of flours.Germination significantly decreased the amylose and starch content in proso millet flours.However,the crude fiber,soluble sugars,free amino acids,?-amylase activity,and bioactive components in flours were increased with germination.Germination increased the brightness(L*),water solubility and swelling degree of waxy and non-waxy proso millet flours,and reduced the density of waxy and non-waxy proso millet flours.During the germination process,part of the starch is hydrolyzed and converted into energy required for germination.This lead to:crystal structure of waxy and non-waxy proso millet was partially destroyed and crystallinity decreased;the onset temperature(To),peak temperature(Tp),and conclusion temperature(Tc)of proso millet increased,the gelatinization enthalpy(?H)decreased;the viscosity of proso millet decreased;the storage modulus and energy modulus of proso millet decreased.In addition,germination decreased the in vitro starch digestibility of waxy and non-waxy proso millet flours and increased the in vitro protein digestibility of waxy and non-waxy proso millet flours.The waxy and non-waxy proso millet flours scatter was mainly distributed on the negative part of PC2.In addition,flours in these flour varieties move with the negative axis of PC1 as the germination time increases. |
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