Título da Tese: Adição de óleos essenciais em coberturas comestíveis: avaliação da atividade antioxidante, aplicação e avaliação da qualidade de produtos de origem animal

Orientador: Prof. Dr. Ivanor Nunes do Prado

 Data da Defesa: 27/02/2018



INTRODUCTION. Beef is among the most consumed meats worldwide. The meat has a high protein content and an abundance of minerals, vitamins and fatty acids, and consumers associate several meat attributes with freshness at display. Among these attributes, color and tenderness are some of the most important purchasing criteria. Meat discoloration results from the conversion of oxymyoglobin (MbO2) to metmyoglobin (MetMb) and an interaction between discoloration and lipid oxidation processes has been demonstrated. Lipid oxidation is the major cause of deterioration in meat quality during storage and processing and the products resulting from the oxidation modify flavor, color, texture and decrease nutritional quality. Thus, to maintain the quality and shelf life of the product, mainly processed, antioxidants are added, being the synthetics the most commonly used. However, due to a growing concern about the safety of synthetic chemicals, the use of natural and bioactive compounds with antioxidant activity is preferred and attracts the attention of researchers. Among the natural antioxidants, essential oils (EOs) are natural compounds extracted from plants that exhibit antimicrobial and antioxidant properties and therefore attract interest as additives in the food industry. Between them, can be cited the EOs of oregano (Origanum vulgare L.) and rosemary (Rosmarinus officinalis L.) that have potential as natural antioxidant in food. The use and choice of EOs should consider the consumer's sensory acceptability of the final product. In fact, due to the strong flavor of EOs, their direct use is often limited, however they can be applied to different technologies, such as edible coatings, in order to improve food quality. Among the compounds used for the development of coatings, alginate stands out for forming strong gels and can be used in meat products. Thus, edible coating can be used to maintain quality and prolong the shelf life of food reducing lipid oxidation, minimizing contact with oxygen, increasing water barrier properties and maintaining food flavor. AIMS. This study evaluated the effects of alginate-based edible coating containing EOs (rosemary and oregano) on meat quality during refrigerate display, as well as the profile and acceptance of the consumer in relation to the final product. MATERIAL AND METHODS. The meat was obtained from crossbred young bulls (½ Angus vs. ½ Nellore), finished in a feedlot and slaughtered at 12-months old. Longissimus dorsi muscle was used, which was filleted in steaks (2.5 cm) and distributed randomly between treatments. The alginate coating (20g/L) was prepared by total dissolution of the alginate at 70 °C. Then the solution was cooled (25 °C) and the EOs (0.1%) were added. Each steak was individually submerged in the alginate solution, allowed to drain the coating excess and then submerged in a solution of calcium chloride (2%, a crosslinking). Each steak, with or without coating, was individually wrapped in polystyrene trays, covered with plastic film and displayed under refrigeration and lighting simulating the conditions of the Brazilian market. Samples were evaluated on days 1, 7 and 14 of display. In order to study the antioxidant potential of the samples (oil, coating and meat) the samples were extracted with methanol and the methodologies of the ferric ion reducing antioxidant potential (FRAP), free radical scavenging (DPPH and ABTS) were employed. To verify the effectiveness of the coatings in delaying lipid oxidation, the TBARs (thiobarbituric acid reactive substances) methodology was used. Besides lipid oxidation, other parameters of quality were evaluated, such as color, pH, weight loss, tenderness, microstructure, consumers’ acceptability and their profile through a questionnaire. Data were analyzed by analysis of variance, using general linear model, and presented as mean 9 and standard deviation or standard error. To verify differences between meat quality and general acceptance the Tukey test was applied. The correlations between sensory attributes were evaluated using the Pearson coefficient. For the consumer analysis Duncan test was used. Cluster analysis was used to determine different consumer segments. Principal components analyses to verify the relationship between the treatments and the sensorial attributes evaluated and the hedonic R index used to verify the preference among the samples. RESULTS AND DISCUSSION. The EOs of oregano and rosemary presented antioxidant activity measured by FRAP of 3.56 and 0.38 mg GAE/g respectively. The scavenging of free radicals ABTS and DPPH of EOs (1: 1000) were 69.94% and 27.31 for oregano and 15.79% and 4.08% for rosemary. This same behavior, a higher antioxidant activity, was also observed in the coating that contained EO of oregano and in the meat to which the coating was applied. In relation to lipid oxidation, it increased during the meat display time (14 days), but more markedly for the uncoated samples. Coatings with EOs reduced lipid oxidation when compared to samples containing only alginate and control sample (uncoated), and the coating with oregano EO was the most efficient. The coloration, parameter L*, decreased in all treatments during the period evaluated. The value of a* also reduced with the display time for the control treatment, while at the end of the 14 days the samples with coatings still had a high value of a *. Regarding the parameter b*, as in the others, there was a reduction of the coloration for the control samples in a more accentuated way and the samples with coating had a more yellow coloration, probably related to the color of the coating. Another parameter evaluated was the chroma, which indicated that the control samples had a paler coloration, which is not desirable for meat. In relation to Hue, the last parameter evaluated related to color, the control meats presented difference when compared day 1 and 14 of display, on the other hand, those that contained coating did not present difference between these days, indicating little color degradation. Regarding pH, there was no difference during the period of 14 days, however, the samples with coating had a higher pH, probably associated to the pH of the coating (± 6.0). The addition of coating significantly reduced the weight loss of meats and little exudate was visible during the exposure. The texture of the meat, that is, the tenderness, was altered during the 14 days, where the meat became tenderness due to the maturation process. Samples with the coating was tender than control during all the evaluated periods, and this may be related to the lower water loss of the coated samples, as well as to a lower oxidation, that leads to the aggregation of proteins and reduces the susceptibility of the proteins to enzymatic proteolysis, thus reducing tenderness. It was also evaluated the microstructure of the meat and the coating and it was possible to observe in the coating without essential oil a smooth and homogeneous structure, while the coatings with EOs presented a heterogeneous structure with oil droplets dispersed throughout the matrix. Another results obtained were the consumer's acceptance of the product, in addition to the profile of these consumers, different market segments obtained by cluster analysis, preference by hedonic R index and principal components analysis. Regarding to general acceptability, the addition of coatings and EOs influenced the attributes of odor, flavor and overall acceptance. Samples containing EO of oregano presented the best results, not differing from those with rosemary in relation to the odor, and the control and standard (coating without EO) in relation to flavor and overall acceptance. EOs also influenced Pearson's correlation results, where flavor and odor were highly correlated with overall acceptance, probably due to the flavor and odor of the oils. About the profile of consumers, 51.1% were men and the majority were younger than 40 years. Most had completed or completing the 10 higher education and the monthly income ranged from 2 to 6 minimum wages. Most consumed beef two to four times a week, while pork was more consumed once a month and lamb once a year. Consumers have indicated that the supermarket is their favorite place to buy, and they prefer fresh meat, besides that the color is the most important attribute at the time of purchase followed by price. Almost half of the participants never consumed edible coatings or did not know about the technology, however the majority expressed good intention to buy products with essential oils. In relation to the use of spices many use oregano (74.4%) while only 22.2% use rosemary, which may explain the better acceptance for the oregano samples. Another way to evaluating consumer acceptance or preference is through the R index, which compares the preference of one sample over another and the meat with coating and EO of oregano was preferred. In relation to cluster analysis, which divides consumers into different niches, this indicated the presence of 3 different groups for odor acceptability. A first group which rejected the odor of all samples, but consisted only of 5.5% of the participants. A second with 25.6% of the participants who preferred the odor of the samples with EOs and rejected the one of the control sample and a third group (68.9%) that did not indicate difference between the treatments. Regarding to flavor for the first group (25.6% of the participants) the samples without EOs were preferred. The second group (27.8%) preferred the samples with EOs. The third group (46.6%) presented high acceptability for all samples. For overall acceptability, the first group preferred the samples with EOs (24.4%), the second group (20%) gave higher scores for treatments without EOs and the third group (55.6%) also gave high scores for all treatments. In the principal components analysis, it can be observed that the attributes of flavor, odor, texture and overall acceptability were located close to the samples with oregano EO, whereas the other treatments were inversely related to these attributes. CONCLUSIONS. The alginate-based coating effectively reduced the weight loss and lipid oxidation of the samples. It reduced the degradation of the meat color and made it tender. The inclusion of EO in the coating increased the antioxidant activity of the product and compared to rosemary the coating that contained oregano presented greater antioxidant activity, less lipid oxidation and greater acceptance by the consumer. Thus, coating with essential oils have a great potential of application in animal products in order to maintain or improve their characteristics during display in the market. Key words: Meat quality, alginate-based coating, meat acceptance, cluster analysis, principal components analysis, hedonic R index.


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