Study On Low-sugar Blueberry Jam Using The Byproducts Of Blueberry Fermentation

The byproducts of blueberry fermentation is a kind of byproducts of blueberrywine after processing, it still contains a lot of nutrients. If processed by a traditionalway, it will not only waste the resources, not fully realized the economic and nutritivevalue of the blueberry, but also cause environmental pollution. And with the rapiddevelopment of blueberry wine processing, there will be more and more blueberryfermentation byproducts. The byproducts will increase pressure of our environment.Therefore, it is of great significance to develop a new product or a new applicationmean of blueberry fermentation byproducts for blueberry production industry andenvironmental protection. In this study, the byproducts of blueberry fermentation isused as raw material, and then use the gel properties of compound thickener todevelop a low-sugar blueberry jam through sensory evaluation and rheologicalprinciples. In addition, the composition of blueberry fermentation byproducts and thelow-sugar blueberry jam are analyzed, the production process of the low-sugarblueberry jam is optimized and its rheological properties is measured. The mainresults are as follows:(1) The composition of the blueberry fermentation byproducts is detected byusing correlation methods of national standards. The results show that the moisturecontent of the blueberry fermentation byproducts up to78.5%, but also rich in dietaryfiber, reaching15.54%. In addition, there is a small amount of protein, fat,carbohydrates and so on. Meanwhile, the constants (K, Na) and trace elements (Ca,Mg, Fe, Zn, Cu), especially Fe, Zn in the blueberry fermentation byproducts aredetected by using the method of ICP-AES. Those elements which are beneficial tohuman are abundant. The content of anthocyanin and flavonol reaches to0.666mg/gand1.962mg/g by spectrophotometry. (2) Sodium alginate and xanthan gum are chosen to mix as a compoundthickener by comparing the method which the smear, elasticity and gels with otherfour thickeners are used alone because of the better stability and workability. The ratioof the compound thickener and the range of concentration are determined by usingrheological method. The rheological measurement results show that the compoundthickener is a kind of pseudoplastic fluid, which show the characteristics of shearthinning and thixotropic. It is a weak gel and can be describe by Casson empiricalmodel. When sodium alginate: xanthan gum equals to4:1, the chewing viscosity,yield stress and consistency coefficient of the system of the compound thickener areall reach the maximum effect. Meanwhile, the elastic modulus and viscous modulusof the system are larger and the hysteresis loop area is smaller relatively. All of theseillustrate that the system is the most stable at the point and conducive to processing.When the concentration of the compound thickener is between2%and5%, thesystem is a suitable viscoelastic system and can be applied for jam processing.(3) The optimum conditions of the low-sugar blueberry jam are established byusing single-factor and orthogonal test. The sensory score is used as the main indexfor product to optimize the formulation and process. The single-factor results showthat when the amount of the compound thickener and citric acid, the sugar-acid ratioand the concentration time are moderate, the sensory evaluation scores of thelow-sugar blueberry jam are higher. The optimum techniques for low-sugar blueberryjam are as follows：compound thickener accounted for3%, the citric acid amount of0.8%, the sugar-acid ratio is1:40and the concentration time is20min. The rangeanalysis and variance analysis illustrate that there are four main factors effecting thesensory quality of the low sugar blueberry jam. Their order is as follows: citric acid>sugar-acid ratio> compound thickener> concentrated time, in which the amount ofcitric acid has a very significant effect on the jam and the sugar-acid ratio has asignificant impact.(4) In low-sugar blueberry jam, the moisture content is still up to70.5%,followed by23.88%carbohydrates and5.19%dietary fiber. The jam also contains small amounts of K, Na, Ca, Fe, Zn, Mg, Cu and other constants and trace elements.Meanwhile, the content of anthocyanins and flavonols are determined byspectrophotometry at different stages of processing. Although these two activeingredients are decreased, the process is preferably retained them in the raw material.The jam has0.087mg/g anthocyanins and0.018mg/g flavonols. From theperspective of rheology, the low-sugar blueberry jam is a kind of pseudoplastic fluid,viscosity increasing with the shear rate decreasing. And the viscosity is significantlyaffected by temperature. As the temperature rises, the viscosity of the systemdecreased significantly. Dynamic rheological measurement displays that low-sugarblueberry jam performs a characteristic of a weak gel, the elastic modulus> viscousmodulus. The elastic modulus and the viscous modulus increase with frequencyincreasing. The soluble solids of the low-sugar blueberry jam is less than40%and theother three kinds of blueberry jam are much higher, and anthocyanins in low-sugarblueberry are higher significantly than others. The sensory evaluation score of thelow-sugar blueberry jam is the highest among the four blueberry jam, containingblueberry aroma, suitable flavors, good spreadability and gelation. In addition, thechewing viscosity of low-sugar blueberry jam is moderate, about6.56Pa·s, thehysteresis loop area is smaller and the flow activation energy is19.216kJ/mol,suitable for processing.