Biochemical studies of cocoa bean polyphenol oxidase

Polyphenol oxidase (EC 1.14.18.1) was isolated and partially purified from cocoa beans. The properties of the enzyme were studied. The Michaelis constant K_m for catechol was 1 × 10^?2 M . The pH optimum of polyphenol oxidase activity assayed with catechol as substrate occurred at pH 6.8 and was characterised by a relatively high thermal stability, 50% of its activity was lost after heating for 40, 25 and 5 min at 60, 69 and 80°C respectively. The optimum temperature for the enzyme activity with catechol as substrate was around 45°C. The enzyme was reactive towards 3-(3,4-dihydroxy phenyl)-DL -alanine, 3-hydroxytyramine hydrochloride and 4-methyl catechol but showed no activity towards tyrosine, p-cresol, and 4-hydroxy-phenol. A rapid deactivation of the enzyme was observed when catechol of concentration > 40 mM was used as substrate. The enzyme activity was inhibited by ascorbic acid, L -cysteine, sodium bisulphite and thiourea.     

Effect of polyphenol and pH on cocoa Maillard-related flavour precursors in a lipidic model system

Polyphenol and pH influence the flavour quality of cocoa beans during roasting. Amino acids and reducing sugars are flavour precursors in cocoa beans, which develop into cocoa-specific aroma through Maillard reactions during roasting. A central composite design was applied to determine the combined effect of polyphenol and pH on the flavour precursors during cocoa roasting at 120 °C for 45 min using a lipidic model system. Polyphenol was added at 40, 80 and 120 g kg⁻¹ and pH was adjusted to 4.5, 6 and 7.5. The response surface methodology revealed that a lower concentration of amino acids and reducing sugars was obtained at higher polyphenol concentration (120 g kg⁻¹) and lower pH value (4.5). Based on the constraints set, the best polyphenol concentration of 43–58 g kg⁻¹ and pH of 7.0–7.5 was found to be optimum for the formation of flavour precursors in this lipidic model study.     

Analysis of cocoa pulp and the formulation of a standardised artificial cocoa pulp medium

Results of analyses of cocoa pulp from the Ivory Coast, Nigeria and Malaysia are reported. These include pH, viscosity and a_w measurements and concentration of soluble sugars, vitamins and anions. Pulp from Malaysian cocoa pods had a higher water content, lower citrate, hemicellulose, lignin and pectin concentration and a higher pH than Ivorian or Nigerian cocoa pods. The composition of a defined cocoa pulp medium which has the same overall composition, pH, a_w and viscosity as cocoa pulp is described. The defined cocoa pulp medium supported the growth of yeasts, lactic acid bacteria and acetic acid bacteria.     

超临界CO_2萃取可可脂与可可色素的实验研究

本课题设计和建立了一套超临界萃取扩大试验装置,实现了用超临界ＣＯ_２同时萃取可可豆壳（或皮）中可可脂及可可色素的工艺。通过静态与动态试验获得了最佳工艺条件。试验结果表明超临界萃取法还具有工艺简单、操作安全、产品质量好、能耗低和萃取率高等优点。     

基于葡萄酒多酚物质水平的葡萄酒鉴别

该文以4个主要葡萄酒产区（宁夏、烟台、甘肃和新疆）、3个酿酒葡萄品种（小味儿多、赤霞珠和马瑟兰）的葡萄酒样品为原料,利用超高效液相色谱-三重四极杆串联质谱技术,分析葡萄酒中37种多酚物质的含量,结合多元统计分析,探讨葡萄酒品种鉴别和产地溯源的可行性。结果表明,不同品种和不同产区葡萄酒中分别有22种和28种多酚化合物含量存在显著差异;经过主成分分析,在不同品种葡萄酒中筛选出咖啡酸、对香豆酸、阿魏酸和花旗松素等16种特征多酚化合物,在不同产区葡萄酒中共筛选出柚皮素、杨梅素、香草酸和根皮素等15种特征多酚化合物;通过Fisher判别分析,不同品种葡萄酒回代检验和交叉检验的整体正确判别率分别为100.0%和91.9%,不同产区葡萄酒回代检验和交叉检验的整体正确判别率分别为100.0%和97.4%。说明基于多酚类化合物指纹的差异可以有效鉴别不同品种和不同产区的葡萄酒。     

Cocoa butter fats and possibilities of substitution in food products concerning cocoa varieties,alternative sources,extraction methods,composition, and characteristics

The current concern for cocoa butter fat as major ingredients of chocolate intake in the World has raised the question of the high price of cocoa butter among all other vegetable fats. Productions of natural cocoa butter fats are decreasing day by day due to the decrease of cocoa cultivation worldwide; moreover, cocoa fruit contains only a little amount of cocoa butter. Therefore, the food industries are keen to find the alternatives to cocoa butter fat and this issue has been contemplated among food manufacturers. This review offers an update of scientific research conducted in relation to the alternative fats of cocoa butter from natural sources. The findings highlights how these cocoa butter alternatives are being produced either by blending, modifying the natural oils or fats from palm oil, palm kernel oil, mango seed kernel fats, kokum butter fat, sal fat, shea butter, and illipé fat.     

Metal contents of some cocoa beans produced in Ondo State,Nigeria

The metal contents in 11 cocoa samples collected from different parts of Ondo State, Nigeria, were determined by the use of atomic absorption spectrophotometry. The moisture and ash contents of the samples were in the range 2.0–3.2% and 2.0–3.8%, respectively, the means being 2.5% and 2.9%, respectively. The mean contents of calcium, magnesium, potassium, sodium, manganese, iron, copper and zinc were 25.5, 5170, 2480, 21, 17, 15.8, 8.2 and 62 μg g^?1, respectively of cocoa bean as purchased. Magnesium was present at much higher levels than the other metals. In some cases the difference between the mean metal content of samples was significant.     

Changes of phenolic compounds and antioxidant capacity in cocoa beans processing

A number of studies have shown that the consumption of cocoa and chocolate products has positive health effects on humans. The object of this research was to monitor changes of total and individual phenolics and antioxidant capacity during the cocoa bean manufacturing. The loss of cocoa phenolics and their antioxidant activity vary with the degree of technological process. The process of roasting and cocoa nib alkalisation had the major influence on phenolic compounds as well as on antioxidant capacity. The roasting treatment resulted in 14% loss of the total phenolics content, while alkalisation resulted in 64% loss of total phenolics content. Procyanidins B1 and B2 as well as (?)‐epigallocatechin were the unstable components, while caffeic acid derivate showed the greatest stability in all technological process. Furthermore, PCA showed that phenolic contents, antioxidant capacity and non‐fat cocoa solids parts of the samples were classified in groups according technological conditions.     

Oxidation of polyphenols in unfermented and partly fermented cocoa beans by cocoa polyphenol oxidase and tyrosinase

Unfermented and partly fermented dried cocoa beans have an excessively astringent and bitter flavour owing to their high polyphenol content. Studies on the remaining polyphenol oxidase activity and the oxidation of polyphenols in these beans have been conducted in relation to two factors, ie incubation time (0, 1, 2, 4, 8 and 16 h) and pH of incubation (3.5, 4.5, 5.5 and 6.5). Owing to unsuccessful polyphenol oxidation during incubation of partly fermented beans, incubation–enrichment treatments were carried out by combining incubation time (0, 8, 16, 24 and 32 h) and addition of crude cocoa polyphenol oxidase and purified tyrosinase from mushroom at 88 and 8800 units g^?1 and pH 5.5. Results showed that the remaining polyphenol oxidase activities of unfermented and partly fermented dried beans were 1 and 0.08% with specific activities of 9 and 1% respectively. The polyphenols of unfermented beans were effectively oxidised by incubation at 45 °C and pH 3.5–6.5 without enzyme enrichment; while those of partly fermented beans required enzyme enrichment. Both crude cocoa polyphenol oxidase and tyrosinase could be used for enzyme enrichment, but tyrosinase seemed to be more effective. © 2002 Society of Chemical Industry     

基于主成分分析的绿豆沙加工用品种筛选

选取北京、河北、东北等地有代表性的12个绿豆品种,测定影响绿豆沙加工的主要营养成分,并对不同品种制成的绿豆沙进行感官评价,然后对各指标进行主成分分析。结果表明,主成分分析提取出4个主成分,累计贡献率达84.380%,可较好反映绿豆沙品质的绝大部分信息。蛋白质、淀粉、硬度、砂质感等为影响绿豆沙品质的主要因子。用这4个主成分代替原来的10个品质因子对绿豆沙进行综合评判,筛选出适宜绿豆沙加工用的品种：中绿10号、保绿942以及冀绿-19-2。     

Effect of fermentation time and drying temperature on volatile compounds in cocoa

The effects of fermentation time and drying temperature on the profile of volatile compounds were evaluated after 2, 4, 6, and 8 fermentation days followed by drying at 60, 70 and 80 °C. These treatments were compared with dry cocoa controls produced in a Samoa drier and by a sun-drying process. A total of 58 volatile compounds were identified by SPME-HS/GC-MS and classified as: esters (20), alcohols (12), acids (11), aldehydes and ketones (8), pyrazines (4) and other compounds (3). Six days of fermentation were enough to produce volatile compounds with flavour notes desirable in cocoa beans, as well as to avoid the production of compounds with off-flavour notes. Drying at 70 and 80 °C after six fermentation days presented a volatile profile similar to the one obtained by sun drying. However, drying at 70 °C represents a lower cost. Given the above results, in the present study the optimal conditions for fermentation and drying of cocoa beans were 6 days of fermentation, followed by drying at 70 °C.     

Occurrence of ochratoxin A in cocoa by-products and determination of its reduction during chocolate manufacture

This work reports an investigation carried out to assess the natural occurrence of ochratoxin A in 168 samples from different fractions obtained during the technological processing of cocoa (shell, nibs, liquor, butter, cake and cocoa powder) and the reduction of ochratoxin A during chocolate manufacture. Ochratoxin A analyses were performed with immunoaffinity columns and detection by high performance liquid chromatography. Concerning the natural ochratoxin A contamination in cocoa by-products, the highest levels of ochratoxin A were found in the shell, cocoa powder and cocoa cake. The cocoa butter was the least contaminated, showing that ochratoxin A seems to remain in the defatted cocoa solids. Under the technological conditions applied during the manufacture of chocolate in this study and the level of contamination present in the cocoa beans, this experiment demonstrated that 93.6% of ochratoxin A present in the beans was reduced during the chocolate producing.     

Physical properties of tempered mixtures of cocoa butter,CBR and CBS fats

Physical characteristics of precrystallised binary mixtures of cocoa butter (CB) and 5, 10, 15, 20, 25 and 30% (w/w) cocoa butter replacer (CBR) or cocoa butter substitute (CBS) were determined. The lipid composition was obtained by chromatography and the solid fat content (SFC) by nuclear magnetic resonance. Tempering was carried out using a lab‐scale agitated jacket vessel reactor. Bars made with tempered samples were submitted to X‐ray diffraction and rupture tests. Snap values of crystallised mixtures decrease with an increase in the amount of alternative fat. X‐ray diffraction patterns confirmed the predominant formation of the beta polymorph habit for CB and beta prime form for CBR and CBS. Mixtures of CB and CBR exhibit chemical compatibility. The knowledge of the snap values and of the variation of SFC with temperature proved to suffice to adequately anticipate the influence of the addition of alternative fats on chocolates physical attributes.     

Effects of incubation and polyphenol oxidase enrichment on colour, fermentation index, procyanidins and astringency of unfermented and partly fermented cocoa beans

Incubation of unfermented and partly fermented cocoa beans in acetate buffer, pH 5.5, at 45 °C increased yellowness, total colour differences and fermentation index value of the cocoa bean powders and decreased cocoa procyanidins (monomers to pentamers), and their astringency. Fermentation index and (–)‐epicatechin content, equivalent to those of fully fermented beans, were reached by unfermented beans after 4–8‐h incubation, but not by partly fermented beans even after 16 h. During incubation of partly fermented cocoa beans enriched with polyphenol oxidase, yellowness and fermentation index value were increased, whilst (–)‐epicatechin was decreased. Tyrosinase had a less significant effect in yellow colour formation, but showed a significant reduction of (–)‐epicatechin and increase in fermentation index compared with crude cocoa polyphenol oxidase. However, both enzymes have similar effects on procyanidin degradation and astringent taste reduction. Incubation of cocoa beans for 16 h increased the cut test score of unfermented and partly fermented beans by 50 and 30%, respectively.     

Bean spreading: A method for pulp preconditioning to impair strong nib acidification during cocoa fermentation in Malaysia

In Malaysia bean spreading was investigated as an alternative method to pod storage for preconditioning of pulp in order to reduce nib acidification during subsequent cocoa fermentation. Harvested pods were broken and the seeds were exposed to quick pulp surface drying either by spreading in full sunshine or by the use of a suitable drier. A decrease in the volume, water and sugar content was observed during spreading, which caused subsequent shallow box fermentation to run similarly to stored pod fermentation, showing a steep temperature increase, absence of an initial anaerobic phase, reduced acetic acid formation and a higher minimum pH value in the nibs. Irregularities in fermentations and practical problems are discussed.