Water Absorption Properties And Volatiles During Cooking Of Foxtail Millet

Millets,the processed products of foxtail millet,are used to make millet gruel.Usually,the flavor aroma,millet color,the stickiness and viscosity of millet gruel are the key index for evaluating the quality of foxtail millet.Among them,flavor aroma is critical to the flavor characteristics of millet gruel,and close related to the cooking quality of foxtail millet.The water absorption is linked to the starch content,gel consistency of millet gruel,and affects the eating quality of foxtail millet.In this study,several varieties of foxtail millet were chosen,and the elite variety Jingu 21 millet was chosen as main research material.The correlation between water absorption properties and the cooking time of different varieties of millets was analyzed,and the volatile components in the millet gruel made from Jingu 21 by different treatments were investigated.Also,the differences of the volatile components among dehulled millets of different colors from four different varieties were studied.The results were showed as the followings:1.An optimum method to remove the free water from the surface of millets by centrifuging to determine the water absorption was determined as 300 rpm for 3 min.2.In order to explore the relationship between water absorption,absorption rate and cooking time of foxtail millet,seven varieties of foxtail millet were tested in this study by centrifuging for the determination of water absorption and absorption rate at different time points within 1 hour.The time required forcracking or "flowering" of the millets were recorded when they were cooked.By studying the curves ofwater absorption and absorption rate of foxtail millet,their correlation and clustering with cooking times,the results showed that:(1)Water absorption of seven varieties of foxtail millet increased rapidly between 0 min to 2 min,thenincreased slower.Their patterns could be divided into two types of curves,the patterns in five varieties followed an S-shaped curve,those of the others tended to be a straight-up line.(2)The water absorption,absorption rate and cooking time between 2 min to 20 min after treatmentsshowed significant negative correlation.When treated longer than 30 min,water absorption and the cooking time still showed a significant negative correlation,whereas water absorption rate and cooking time showed a positive correlation.(3)The water absorption at the early stage in foxtail millet was faster than the later stage.All thevarieties showed a turning point of water absorption at 2 min,when the water absorption rate peaked.Two minute water absorption and its rate appeared to be the absorption characteristics of foxtail millet.3.In order to determine the volatile components of millet gruel,Jingu 21 millet was cooked for 20 min and volatiles were analyzed with HS-SPME-GC-MS.The main results were:(1)A total of 21 key volatile compounds were detected using HS-SPME-GC-MS,and 13 flavor aroma compounds were detected.These compounds included aldehydes(9 compounds),phenols and alcohols(2 compounds),heterocycles(2 compounds),acids and esters(3 compounds),hydrocarbons(5 compounds).(2)Aldehydes and hydrocarbon were main volatile components of millet gruel,and the aldehydes played important roles to form the flavor aroma of millet gruel.4.A set of different treatment methods were used,including different cooking time(0,10,20,30,40 min),different pH(pH 6,pH 7 pH 8),millet and millet flour,different seed color(dark yellow,light yellow,green,white),to study the changes of volatile components in the millet gruel,the main results were:(1)During 0 to 40min cooking,the longer the cooking time,the higher the concentration of volatile components.(2)The pH value of water from 6 to 8 had no obvious impact on the aroma of the millet gruel.(3)Millet flour released more aroma than the non-milled millets when the same amount(weight)of material was used.(4)By studying the volatile components from dehulled millets of different colors from different varieties,we found that the volatile components in Jingu 21 millet(dark yellow)had a striking difference compared to Daqinggu millet(gray),and the Jingu 36 millet(light yellow)had no significant difference from Zhishenggu millet(white).(5)The level of 6-Methyl-5-heptene-2-one in Jingu 21(dark yellow)was significantly higher than those in the other three varieties,and reached highly significance compared with Daqinggu(gray).To sum up,water absorption,water absorption rate of millets were closely related to the cooking time of millet gruel.The flavor aroma of millet gruel may not be contributed by a single flavor compound,but rather by the combination of several or many different flavor components.This study would provide a foundation for further research on improvement of cooking quality of foxtail millet in the future.