Detection of bissap calyces and bissap juices adulteration with sorghum leaves using NIR spectroscopy and VIS/NIR spectroscopy

Abstract

Adulteration of bissap calyces and juices (‘sobolo’) with sorghum leaves presents a potential decrease in nutritional benefits to consumers. This study investigated the detection of bissap calyces and juices adulteration with sorghum leaves using near-infrared (NIR) and ultraviolet-visible (VIS/NIR) spectroscopy. Eight samples of bissap calyces-sorghum leaf formulations were prepared using eight concentrations (0, 5, 10, 20, 30, 40, 50 and 100 %) w/w. Each sample was prepared in cut, whole and powder forms, respectively. The samples were then used to prepare bissap juices in triplicates. The bissap calyces-sorghum leaf formulations were analyzed with NIRS, while bissap juices were analyzed with VIS/NIR spectroscopy. Results from the physicochemical analysis showed that the unadulterated samples had lower pH and higher (brix, titratable acidity, and total phenolic content), with no intense color change for all forms when compared to adulterated samples. PCA showed no difference between adulterated and unadulterated samples based on forms and concentrations. LDA showed a 100 % classification for all cut samples and some misclassifications for whole and powder samples for both NIR and VIS/NIR spectroscopy. Also, there were observable differences between adulterated and unadulterated juices produced from cut forms. PLSR models predicted different concentrations of adulterants present in both bissap calyces and juices. Bissap juices adulterated with sorghum leaves are not easily detectable and have reduced concentrations of some beneficial nutritional compounds present in sobolo. NIR and VIS/NIR spectroscopy, combined with chemometric techniques such as PCA, LDA, and PLSR, as a rapid detection technique, showed good potential for sobolo authentication.