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Title: Dark chocolate : effects of particle size distribution and composition on physical qualities and flavour volatiles release
Author: Afoakwa, Ohene Emmanuel
ISNI:       0000 0000 3654 7375
Awarding Body: University of Strathclyde
Current Institution: University of Strathclyde
Date of Award: 2008
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Rheological, texture and melting properties of dark chocolates were studied varying particle size distribution (PSD) [D₉₀ (90% finer than this size) of 18, 25, 35 and 50 µm], fat (25, 30 and 35%) and lecithin (0.3 and 0.5%) contents. Fat pre-crystallisation systems during tempering and fat bloom development were also investigated, and influences on product microstructure, texture, appearance (colour and gloss) and melting characteristics elucidated. Flavour volatile release from varying product matrices were characterised and quantified. Rheological, textural and melting properties were examined quantitatively using Haake rheometer, texture analyzer and differential scanning calorimetry respectively; surface colour and gloss with a HunterLab Colorimeter and Gloss meter respectively; microstructures by light, stereoscopic binocular and scanning electron microscopy; and flavour volatiles quantified by GC-MS and GC-Olfactometry. Multivariate regression, correlation and principal component analyses were employed to explore interrelationships among the rheological, textural and melting characteristics. The PSD, fat and lecithin contents significantly affected all rheological and textural parameters, with significant interactions among factors. Increasing particle size reduced all rheological and textural parameters with greatest effects noted with 25% fat and 0.3% lecithin, which reduced with increasing fat and lecithin contents. Statistical analyses revealed that fat exerted the greatest effect on variability in rheological, textural, melting properties and appearance followed by PSD and lecithin. Microstructures revealed wide variations in crystalline network structure and inter-particle interaction strengths related to PSD, fat content and temper regimes. Correlation (r = 0.78-0.99) and regression coefficients (R² = 0.59-0.99) suggested rheological, textural and melting index parameters had inter-relationships predictive of character. Effects of temper regime were noted with varied influences on product character, and hypotheses proposed for mechanisms of bloom development in under-tempered products. Finally, flavour-active volatiles were characterised and their release quantified with data suggesting potential effects of matrix structure and lipophilic-flavour interactions.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral