The Development of Spectroscopic Methods for the Detection of Adulteration in Coconut Water

Abstract

Adulteration of food, defined as the fraudulent manipulation of the contents of products for economic gain, is a practice that is both costly and potentially hazardous to the health and cultural sensitivities of consumers. It comes in many forms, the most common of which are undeclared substitution of a product with less expensive and lower quality alternatives or the addition of external products to alter organoleptic characteristics. Coconut water is refreshing tropical beverage which has greatly risen in popularity in the last five years. Its popularity, along with its high manufacturing and retail costs, has led it to be highly susceptible to fraudulent practices such as stretching and mislabeling. Currently, the common methods of detecting adulteration often involve enzymatic reactions or time consuming and resource intensive isotope fractionation methods. Spectroscopic technologies have the potential of providing versatile and accurate measures of adulteration in an inexpensive and high-throughput manner, and could therefore be used as screening methods in a commercial setting. In this work, spectroscopic technologies are presented to provide solutions in two scenarios: the adulteration of coconut water with bovine milk, and stretching with water while using various ratios of glucose, sucrose and fructose as masking agents. Using FTIR combined with PLSR, linear quantification of bovine milk in coconut water was achieved at a concentration of ~0.3%. In comparison, HPLC-RI was unable to match this despite a complete separation of lactose, the target analyte, from sugars naturally present in coconut water. Additionally, Raman spectroscopy in combination with chemometrics was found to be a powerful tool in studying the masking of diluted coconut water. When dilution was masked by keeping the total sugar concentration constant with a single sugar, linear quantification within 5% was readily achieved. However, masking using a mixed sugar solution emulating the natural concentrations of each sugar lessened the ability of Raman spectroscopy to detect this form of masking due to the overwhelming presence of peaks attributed to sugars. Finally, NMR was chosen as a comparative method to study the masking of coconut water with a mixed sugar solution, and was able to clearly detect stretching even when individual sugar concentrations were kept constant. An adulteration related drift in the chemical shift of malic acid signals was also observed, providing potential for further research.

Date of Award	1 Aug 2018
Original language	English
Awarding Institution	The University of Manchester
Supervisor	Royston Goodacre (Supervisor) & David Ellis (Supervisor)