Study On The Quality Change In The Process Of Zinc-Rich Wheat Steamed Bread Making

Zinc,one of the most essential trace elements,is closely related to human health.Zinc deficiency can cause a series of diseases and even life-threatening.As one of the world's three major food crops and the staple food of the world's people,wheat is considered to be an important carrier of zinc biofortification.In China,the content of zinc in the wheat grain gained in the main wheat producing areas is mostly less than 30 mg/kg,which is lower than the international recommended standard of zinc content in the grain of zinc-rich wheat(40-60mg/kg),and cannot meet the nutritional needs of the population that takes wheat as the staple food.The edible route of wheat is always include two main steps: grinding the wheat grain into flour and the later related food making,during which the bran with the highest zinc content is often discarded accompanied by the large loss of zinc in wheat grains.Therefore,bran can be applied to the processing of steamed bread to improve the content of zincand increase the utilization rate of zinc in wheat grains.Studies have shown that foliar application of zinc fertilizer with reasonable spraying methods and suitable concentration,was an effective means to rapidly increase the content and the bioavailability of zinc in wheat grain.In this experiment,zinc fertilizer was respectively sprayed at the jointing stage,flowering stage,early and late stage of wheat growth to bring about zinc biofortification of wheat.At the same time,in order to further increase the zinc content in the steamed bread,the bran,which has the highest zinc content in the wheat grain,was processed into large(60 mesh),medium(80 mesh)and small(100 mesh)particle size by an ultrafine pulverizer,and then supplemented to the flour at five different substitution levels(0%,5%,10%,15% and 20%)under each particle size condition to prepare bran flour to increase the zinc content in the flour.Under the premise of application of zinc spray fertillizer,we studied the effect of different particle size and substitution levels of bran on flour quality and dough properties by determinating the dough rheological properties of bran flour that has a different bran content,after which,we can chose the optimal particle size and substitution levels of bran via considerating both the evaluation of bran bread products and the level of zinc content in the bran bread.We aimed at bring the biofortification of zinc in wheat grainfrom farmland to table to obtain wheat bran steamed bread that with the zinc content in line with enhanced standards,so that we can provide people a way to supplemented zinc through staple food in this experiment.Results are as follows:(1)Compared with the blank control group(37.1 mg/kg),the zinc content of wheat grain in the zinc fertilizer spraying group was significantly increased(54.7 mg/kg).Compared with the control group(7.5 mg/kg),the zinc content of wheat flour in the zinc-spraying group was significantly increased(11.9 mg/kg).After applying zinc fertilizer,the zinc content in wheat grain increased by 47.4%,and the zinc content in flour increased by 58.7%,both reaching the target content of biological enhancement.(2)There were significant differences of the zinc content in different processed components during the milling process of zinc-rich wheat grains.The variation of zinc content in each powder path was: 3B>2B>1B,3M>2M>1M.Among them,the zinc content in bran was the highest,which was significantly higher than that in other processed components.(3)With the increase of the bran content,the flour quality gradually deteriorated.Under the same bran content,the quality of flour with different grain bran sizes changed as follows:the flour with 80 mesh bran content was the best,while the flour with 60 mesh bran content was the worst;In addition,the change rule of zinc content in wheat bran flour was as follows:the flour with 60 mesh bran had the highest zinc content,while the flour with 100 mesh bran had the lowestzinc content.(4)The texture data and sensory evaluation of the wheat bran steamed bread showed that the specific volume and comprehensive sensory score of the steamed bread decreased with the reduction of wheat bran particle size.With the increase of wheat bran content,the surface color of wheat bran steamed bread became darker,and its internal structure and taste became worse.The wheat bran steamed bread with wheat bran content of 5% and grain size of 80 mesh had the highest comprehensive quality score.Under these conditions,the zinc content in the bran steamed bread was 40.2mg/kg,while that in the control group was only 25.8mg/kg.Compared with the other steamed bread,the zinc content in the bran steamed bread increasd.by55.8%,reaching the purpose of increasing the zinc content in the steamed bread.