Preparation And Quality Evaluation Of Instant Powder Of Yam

Yam is traditionally used both as medicine and food,as recommended by the Ministry of Health.The instant yam powder is nutrition-rich and convenient to eat.Based on the principal component analysis and analytic hierarchy process,we established a mathematical model for the comprehensive evaluation of instant yam powder.We investigated the effects of heat treatment on the physical and chemical properties of yam powder,and comprehensively evaluated the preparation of instant yam powder by different approaches,including steaming at atmospheric pressure,enzymolysis and spray freeze drying.The results are as follows:（1）The principal component analysis method and the analytic hierarchy process were used to generate a mathematical model for the comprehensive evaluation of instant yam powder.The model is as follows:S=0.0214*StdX₁+0.0728*StdX₂+0.0553*StdX₃+0.1088*StdX₄+0.1010*StdX₅+0.1747*StdX₆+0.3292*StdX₇+0.0321*StdX₈+0.1047*StdX₉.（2）The effects on the physical and chemical properties of yam powder of different heat treatments were determined by steaming or stewing yam at atmospheric pressure.The results showed that the wettability and dispersibility were improved by heat treatment,which decreased from 7.77 min,4.68 min to 2.11 min and 0.52 min,respectively.After heat treatment,the pasting temperature,peak viscosity,minimum viscosity,breakdown value,and final viscosity of yam flour were decreased,while the iodine blue value increased with the increase of heat treatment time.The content of fast digestible starch and slowly digestible starch in yam powder without heat treatment was relatively low,while the content of resistant starch was the highest.The main component of yam powder after the heat treatment was fast digestible starch,while slowly digestible starch and resistant starch was low in amount.The apparent viscosity of heat-treated yam flour was negatively correlated with the shear rate,exhibiting shear thinning.Heat treatment destroyed the structure of yam flour,decreased its internal order and made its appearance irregular.It was also found that the change of color caused by atmospheric boiling was less than that caused by atmospheric steaming,while the change of solubility caused by atmospheric steaming was less than that caused by atmospheric boiling.After steaming at atmospheric pressure,the solubility of yam flour increased from 16.05 g/100g to 17.21 g/100g.The boiling treatment resulted in a great decrease in the content of functional components,the contents of polysaccharides,total polyphenols,total flavones and allantoin decreased from 2.667 g/100g,0.076 g/100g,0.084 g/100g,0.445 g/100g to1.753 g/100g,0.070g/100g,0.071 g/100g and 0.288 g/100g,respectively.While the steaming treatment resulted in the loss of total polyphenols and flavonoids,which decreased from 0.076 g/100g,0.084 g/100g to 0.055 g/100g and 0.061 g/100g,respectively.（3）Based on the mathematical model mentioned above,we systematically evaluated the overall quality of instant yam powder obtained by different preparation processes.We found that the instant yam powder prepared by steaming at atmospheric pressure+enzymolysis+spray-freeze-drying was of the best quality（comprehensive score:0.84）,followed by steaming at atmospheric pressure+spray-freeze-drying（comprehensive score:0.05）,and instant yam powder treated by steaming at atmospheric pressure+hot-air-drying was of the lowest quality（comprehensive score:-0.90）.