The Effect Of Ultrasound Coupled With Citric Acid Solution For Rapid Debittering On Physical And Chemical Indexes Of Bitter Almonds

Debitterizing is a necessary process in the processing of apricot kernel.The traditional method of debitterizing takes a long time,consumes a lot of energy,and the nutrient loss of apricot kernels is serious,which discharge a large amount of waste water,wasting the resources and polluting the environment serious.Consequently,finding a method of debitterizing which are low in energy consumption,high in efficiency and reduce the loss of nutrients during processing is a key technical problem faced by the apricot kernel industry.Based on the primary study in our laboratory,it was found that ultrasound can accelerate the removing bitterness and shorten the time of apricot kernels.The quality and taste of apricot kernels are different after bitterness-removal by different solutions exposured ultrasound.And the reason still remains unclear.Therefore,the aim of this study was firstly to investigate the relationship between the bitterness and the amygdalin content so as to scientifically judge the end point of apricot kernel.And on this basis,deeply studies were conducted on the effects of pH on the quality characteristics of the apricot kernels debitterized by ultrasound irradiation,in order to provide a theoretical basis for the selection of debitterizing solvents.In order to reduce the waste of apricot kernel resources and promote the development of apricot kernels industry.The main results of this dissertation are as follows:1.Sensory evaluation was conducted with quinine as the standard to evaluate the debitterized apricot kernels,the results showed that the content of amygdalin in apricot kernels was positively correlated with the bitterness.The bitterness threshold of amygdalin in apricot kernel is 0.91 mg/g(dry basis),when the content was lower than 0.91 mg/g,no bitterness can be tasted.In the apricot kernel processing,high performance liquid chromatography(HPLC)can be used to detennine the residual amount of amygdalin in apricot kernels to scientifically judge its degree of removing debitterness.2.The effects of pH on the color,quality and physicochemical properties of the apricot kernels caused by ultrasound irradiation were investigated.The results indicate that the citric acid solution with a pH value of 5 had the fastest debitterizing speed,only demanding 90 min.The apricot kernels obtained under the optimized conditions have the highest sensory score and best taste.And the loss of nutrients such as protein,reducing sugar and total phenols in apricot kernels is also less and the original nutrients in apricot kernels is retained to the greatest extent.3.Ultraviolet spectroscopy,fluorescence spectroscopy,SDS-PAGE,circular dichroism analysis and thermal analysis were used to study the effect of pH on the crude protein of the apricot kernels debitterized by ultrasound irradiation.The results showed that the molecular weight of crude protein of apricot kernel was 22-43 kDa,the citric acid solution with different acidity changed the molecular structure and secondary structure of crude protein.The internal structure of the crude protein of apricot kernel was less changed,not loose,and had little effect on the crude protein when the citric acid solution with a pH of 5,6,and 7.4.The effects of pH on the amino acids of the apricot kernels debitterized by ultrasound irradiation were also studied.And the results showed that the apricot kernels contained a variety of amino acids,a complete range of essential amino acids and non-essential amino acids,and all samples had higher levels of glutamic acid and aspartic acid.The standard pattern proposed by WHO/FAO was used as a reference,and investigations were conducted with correlation,principal component,clustering and other analytical methods to comprehensively evaluate the amino acids in all samples.The samples debitterized by the citric acid solution with pH of 5 had the highest score,that is,the amino acids nutritional value of apricot kernels is the best.This study can provide a theoretical basis for the selection of debitterizing solution in the process of apricot kernels debitterizing,and further achieve the purpose of shortening the time required for debitterizing,reducing nutrient loss and reducing energy consumption.