Effect of the degree of milling on the physicochemical properties,pasting properties and in vitro digestibility of Simiao rice

Simiao rice is a variety of long-grain Indica rice popular in South China.However,researches on the milling technology of Simiao rice are limited.The effect of different degrees of milling(DOMs)of Simiao rice(0-12%)were evaluated in terms of the physicochemical properties and in vitro starch digestibility of the rice.The results showed that,as the DOM increased from 0 to 12%,the head rice yield(HRY)and the content of protein,lipid,dietary fiber,vitamin B1,vitamin E and niacin nonlinearly decreased,while the content of total starch and amylose and paste viscosity parameters nonlinearly increased.The differences in chemical constituents between the brown and milled Simiao rice with different DOMs lead to the variation in their pasting properties and in vitro digestibility.Because of lower content of slowly digestible starch(SDS)and resistant starch(RS),milled Simiao rice exhibited greater digestibility and a higher estimated glycaemic index(EGI).The EGI of Simiao rice ranged from 77.98 to 85.55,and remained almost constant(approximately 84)when the DOM was above 4%.Correlation analysis indicated that the EGI had strong negative correlations with lipid,protein,dietary fiber and RS,but a positive correlation with amylose.These results provide theoretical guidance for the production of Simiao rice with desired physicochemical properties and digestibility by adjusting the DOM.

Effect of the degree of milling on the microstructure and composition of japonica rice

The effect of the degree of milling(DM)on the distribution of the residual bran layer on the surface of rice grains and subsequent rice quality is essential for rice milling technology.This study used scanning electron microscopy(SEM)and energy dispersive spectroscopy(EDS)to examine the microstructure of japonica rice grains,the microstructural changes in different bran portions after milling,and the content and distribution changes of the elements and nutrients in rice after milling to identify the components that can quantify bran residue according to DM.The SEM results revealed that the thickness of the bran layer and the depth of the grooves in different parts of a rice grain varied,while the depth of the grooves differed between varieties.When DM was 12%,aleurone layer(Al)cells embedded in endosperm(En)remained in the dorsal area.It was speculated that this was the reason why there was no significant difference in bran degree when the DM estimated via grain weight loss increased from 10%to 14%(P>0.05).The EDS elemental mapping image showed the qualitative distribution of the elements,which was condensed in the bran and uniform in the En.The compositional changes revealed that milling caused the loss of rice nutrients,and the loss rate of DM at 0–10%was more serious than that of DM at 10%–14%.Higher DM(>10%)could remove marginal bran from the dorsal groove.Therefore,the crude protein,ash,crude fat,dietary fiber,vitamin B1(VB1),and vitamin B2(VB2)content did not change significantly(P>0.05),while the magnesium(Mg),kalium(K),and phosphorus(P)levels decreased substantially(P<0.05).The microstructural and compositional changes indicated that the DM estimated via the grain weight loss increased from 2%to 10%,with the bran decreasing progressively.The DM estimated via the grain weight loss increased from 10%to 14%,with minimal changes in the residual bran in the dorsal grooves of the rice grains,while the Mg,P,and K levels presented precise DM indices during the rice milling process.This result will provide a theoretical reference for the accurate evaluations of DM.

Influence of Moisture Content,Variety and Parboiling on Milling Quality of Rice Grains

The effects of moisture content （8%, 10%and 12%）, variety （Tarom and Fajr） and parboiling on milling quality of rice as a function of milling recovery （MR）, head rice yield （HRY）, degree of milling （DOM） and whiteness were investigated. The parboiled grains was prepared with three soaking temperatures of 25 oC, 50 oC and 75 oC and three steaming times of 10, 15 and 20 min. As a result of parboiling, the increasing rates of MR and HRY values were 7.8%and 14.3%for Tarom and 9.8%and 10.0%for Fajr, respectively, and the decreasing rates for DOM and whiteness were 6.6%and 10.8%for Tarom and 6.8% and 10.5% for Fajr, respectively. Moreover, decreasing moisture content to 8%maximized MR （75.8% for Tarom and 74.3% for Fajr） and HRY （65.8% for Tarom and 57.0% for Fajr） while increasing that to 12%revealed maximum values of DOM （6.1%for Tarom and 6.2%for Fajr） and whiteness （24.8%for Tarom and 28.2%for Fajr）.