Estudo do melhoramento do sabor de cacau (Theobroma cacao L.) utilizando polifenoloxidase extraida da pinha (Annona squamosa L.) e tratamento termico não convencional

AUTOR(ES)
DATA DE PUBLICAÇÃO

1999

RESUMO

Considerable variations in the taste of cocoa occur according to the region of production, some regions producing excessively acid, bitter and astringent cocoa beans. In general, cocoa beans produced in Brazil and Malaysia are characterized by excessive acidity as compared with those from East Africa, limiting the amounts of these beans that can be used in formulations. The presence of acetic and lactic acids, separately or combined, has been shown to be the principal cause of this excessive acidity. On the other hand, according to those who commercialize brazilian cocoa beans, an important percentage of national beans are currently insufficiently fermented (violet color). Compared to well fermented beans (brown color), such peans present an increase in astringency and bitterness. This increase can prevent the perception of other, favourable flavours. Assuming such deficiencies in the organoleptic qualities of brazilian cocoa as compared to that of other producer countries, this research aimed at developing some technological resources to improve the taste characteristics of brazilian coca. One of the resources used was the heat treatment of the beans after roasting, aimed at reducing the acetic acid content, at the same time following the behaviour of the aromatic compounds and their principie precursors. Partially purified polyphenoloxidase (PPO), extracted from Annona squamosa L pulp, was used to reduce the content of phenolic substances. In the first part of this research, the cocoa nibs (Theobroma cacao L, Forasteiro variety, cultivated in Bahia state, Brazil) were roasted at 150°C for 38 minutes. The roasted nibs were then submitted to a heat treatment according to a complete factorial (22) central compound rotational design (CCRO). The independant variables were temperature (from ~O to 75°C) and time (from 20 to 90 minutes). The dependant variables (responses) used to evaluate the assays were: amount of acetic acid, reducing sugars, terminal amino groups and behaviour of the aromatic profile. In the second part, autoclaved nibs (121°C/15 min.) and non-autoclaved, raw, insufficielitly fermented dried nibs, of the same origin, were imbibed in a solution containing 200U/min/ml of enzyme for 30, 60, 90, 150, 210 and 360 minutes at 23°C and pH 6. The nibs were dried and ground and subsequently deffated. The defatted cocoa powder was quantitatively analyzed for total phenols, tannins, anthocyanidins 8nd flavan-3-ols. After heat treatment, a significant decrease in the acetic acid content was observed in nibs heated for more than 70 minutes at initial temperatures in the heating jacket in the range from 75 to 85°C. A significant decrease in reducing sugar content occurred with heat treatments above 75°C for short times (10-15 min) and of about 50°C for longer time periods (more than 85 min). The concentration of terminal amino groups decreased significantly during post¬roasting heat treatment at temperatures above 45°C and times of about 80 minutes, although it was apparent that the effect of temperature was insignificant in comparison with the effect of time. The behaviour of the aromatic compounds (pyrazines) was analysed using response surface methodology, but significant predictive equations were not obtained, the lack of fit of the experiment being very great and R2 very low. This lack of fit probably occurred due to other factors. An analysis of the results obtained in the assays aimed at reducing the polyphenolic content, showed that there was no significant difference (p<0.05) between treatment times of 210 and 360 minutes, so the material used in the sensorial test was that obtained with 210 minutes of treatment. The phenolic content of non¬autoclaved, enzymatically treated (210 min) nibs, decreased by 15% as compared to the untreated samples. The decrease in phenolic content of autoclaved enzymatically treated nibs was 24%. With respect to the tannin content, the decrease in PPO treated non-autoclaved nibs was 15% and in autoclaved treated nibs, 26%. The loss of anthocyanidins in treated non-autoclaved nibs was 18% and in autoclaved nibs, 51 %. The concentration of flavan-3-0Is fell by 10% in non¬autoclaved nibs and 23% in autoclaved nibs. The enzyme treatment resulted in an alteration in the taste of autoclaved insufficiently fermented nibs, decreasing the astringency and bitterness. This sensory alteration was perceived in the acceptance test, there being a significant difference at the 5% level in the hedonic evaluation between the product formulated with the treated sample and that formulated with the non-treated sample.

ASSUNTO(S)

sabor cacau calor fenois

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