EFFECTS OF ALKALIZATION AND ROASTING ON FREE AND BOUND PHENOLIC COMPOUNDS IN COCOA NIBS AND SHELLS
Open Access
- Author:
- Dai, Qiaoqiao
- Graduate Program:
- Food Science
- Degree:
- Master of Science
- Document Type:
- Master Thesis
- Date of Defense:
- September 06, 2017
- Committee Members:
- Gregory Ray Ziegler, Thesis Advisor/Co-Advisor
Joshua D Lambert, Thesis Advisor/Co-Advisor
Helene Hopfer, Committee Member - Keywords:
- COCOA
PHENOLICS
BOUND
ALKALIZATION
ROASTING - Abstract:
- Cocoa nibs are a rich source of polyphenols, especially flavanols. Cocoa shells, generally considered a by-product of cocoa processing, have low economic value. Previous research has focused on the polyphenols that can be extracted directly from nibs with aqueous-organic solvents, the so-called “free” forms. In grains, fruits, coffee beans, and nuts, many phenolic compounds exist in significant amounts bound to plant fibers through ester and ether bonds. Since cocoa fiber has been shown to have antioxidant capacity, and cocoa shell is a rich source of dietary fiber, it was hypothesized that both cocoa nib and shell contain bound phenolics. This study aimed to identify and quantify the bound phenolic compounds in both cocoa nib and shell. In addition, the effects of the industrial cocoa processing operations, alkalization and roasting, on the phenolic content in cocoa beans were investigated. Raw Trinitario cocoa beans were alkalized for 0, 60, or 120 minutes. They were then dried and roasted for 30 minutes at 110, 130, or 150 °C. This 3 x 3 experimental design allowed analyses of both main factor and interaction effects. The nib and shell were then separated, each component was ground, and the pH and color measured. The shell and nib powders were defatted, and the free phenolics were extracted. Bound phenolics were liberated by alkaline hydrolysis with NaOH and extracted in a manner analogous to the free phenolics. Analyses by HPLC coupled with UV and electrochemical (ECD), and UPLC coupled with mass spectrometry (MS/MS) detections were conducted to identify and quantify the major phenolic compounds in each fraction. Principal component analysis (PCA), multivariate analysis of variance (MANOVA), analysis of variance (ANOVA), and quadratic regression were used to analyze the phenolic profile. Three flavonoids, (-)-epicatechin, (+)-catechin, and quercetin, and five phenolic acids, 4-hydroxybenzoic, protocatechuic, chlorogenic, p-coumaric, and ferulic acids, were identified and quantified in free and bound forms. For non-alkalized cocoa roasted at 110°C, the total phenolic content (TPC) of the free fractions (70.9 mg gallic acid equivalents [GAE]/g defatted nib and 18.85 mg GAE/g defatted shell) was close to literature values, and the shell contained higher bound TPC (61.34 mg GAE/g) than the nib (47.75 mg GAE/g). These non-alkalized cocoa beans roasted at 110°C contained 116.31 μg/g and 164.08 μg/g of bound (-)-epicatechin, and 125.72 μg/g and 115.28 μg/g of bound (+)-catechin in nib and shell, respectively. The majority of phenolic acids were in bound forms in both cocoa nib and shell, and, the most abundant bound phenolic acids in nib was 4-hydroxybenzoic acid (397.11 μg/g), whereas in the shell, it was protocatechuic acid (363.03 μg/g). There were significant differences in phenolic contents between free and bound fractions, nib and shell fractions, and water soluble and water insoluble fractions. Alkalization and roasting had significant effects on TPC, (-)-epicatechin, and (+)-catechin contents in nib in free fractions, but not in their bound fractions suggesting that these bound phenolics were likely less vulnerable during alkalization and roasting. Specific effects of alkalization and roasting on other phenolic compounds were specific to each particular compound and to each fraction (i.e., nib vs. shell, free vs. bound, and water soluble vs. insoluble extract fractions).