Evaluation of Yogurt Quality during Storage by Fluorescence Spectroscopy

Haifeng Sun,Hao Zhang,Wei Zhang,Jiandong Hu,Juanhua Zhu,Ang Wu,Ling Wang

doi:10.3390/app9010131

Abstract

The physico-chemical parameters including pH and viscosity, and the fluorescence signal induced by fluorescent compounds presenting in yogurts such as riboflavin and porphyrin were measured during one week’s storage at room temperature when five brands of yogurt samples were exposed to ambient air. The fluorescence spectra of yogurt showed four evident emission peaks, 525 nm, 633 nm, 661 nm, and 672 nm. To quantitatively investigate the quality of yogurt during deteriorating, a calculating method of the average rate of change (ARC) was proposed to study the relative change of fluorescence intensity in the spectral range of 600 to 750 nm associated with porphyrin and chlorin compounds. During the storage, the time evolution of two ARC, pH value, and viscosity were regular. Moreover, the ARC showed a good linear relationship with pH value and viscosity of yogurt. Further, multiple linear regression (MLR) models using two ARC as independent variables were developed to verify the dependence of fluorescence signal with pH value and viscosity, which showed a good linear relationship with an R-square of more than 85% for each class of yogurt. The results demonstrate that fluorescence spectra have a great potential to predict the quality of yogurt.

Highlights

Yogurt, as one kind of dairy products, has attracted more and more attention in recent years, especially since various brands of yogurt contain special strains of “probiotics” that can help boost the immune system and promote a healthy digestive tract
The characteristic fluorescence spectra of yogurt consist of a broadband spectrum in the wavelength region of 500 to 600 nm with a peak at 525 nm attributed mainly by the riboflavin and Maillard products of raw milk and several narrow emission peaks in the region of 600 to 750 nm caused by the porphyrin and chlorin compounds existing naturally in yogurt
The decreasing tendency of K622/633 and the increasing tendency of K661/672 indicate the photodegradation of porphyrin and chlorin compounds

Summary

Introduction

As one kind of dairy products, has attracted more and more attention in recent years, especially since various brands of yogurt contain special strains of “probiotics” that can help boost the immune system and promote a healthy digestive tract. Yogurt provides rich nutrient elements from milk and varieties of vitamins produced in the process of bacterial fermentation of milk, which can contribute to health care and prevent diseases [1]. With the fast development of the yogurt industry, various types of yogurt emerge in the market, followed by the difference in yogurt quality and flavor. The accurate identification of different yogurt species and the quantitative evaluation of yogurt quality become very important for the development of the dairy industry. The traditional detection methods for yogurt quality include biological and chemical methods, such as the standard plate colony counting method for bacterial plate counts and chromatography-mass

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