Assessing the Impact of Preharvest and Postharvest Factors on Cocoa Bean Quality Using Standard Methods and Novel Handheld Nir Spectrometer Coupled with Chemometrics

Abstract

Cocoa bean quality is influenced by preharvest and postharvest factors. Rapid evaluation is therefore required to aid in decision-making. In this study, four experiments were performed separately using a completely randomized design with age class, pollination type, production method, cocoa-producing region and geographical location as the main factors. The novel handheld NIR spectrometer combined with multivariate qualitative algorithms gave a 100 % classification rate for cocoa beans; from the seven cocoa-growing regions in Ghana, four geographical locations in Africa, fermented against unfermented, and organic against conventional. Quantitatively, the performance of the regression models for simultaneous prediction of fermentation index, pH, fat, polyphenols, flavonoids, and antioxidant capacity was in the range of: 0.87≤R2cal≤0.99 and 0.88≤R2pre≤0.99 in calibration and prediction sets respectively. Cocoa beans' physical, chemical and mineral properties were significantly impacted by age of the cocoa tree and pollination type. Calcium, magnesium, phosphorus and potassium were found in the range of 111.44 - 125.23, 238.79 - 249.05, 528.24 - 541.40 and 473.05 - 631.34 mg/100g, respectively whereas sodium, iron, copper and zinc were found in the range of 7.08 - 11.54, 5.80 - 8.83, 1.34 -3.33 and 2.36 - 5.14 mg/100 g, respectively for cocoa bean categories examined. Generally, the NIR spectroscopic technique developed correlated well with the wet chemistry method (R2 = 0.93). The outcome of the study reveals that the handheld NIR spectroscopic technique can be used for rapid, non-destructive and on-site measurement of cocoa beans quality parameters qualitatively and quantitatively.