Protein bars have become a popular option among consumers to increase protein content in their diets. Since there is a large market for protein bars, many factors must be considered when creating a protein bar that both satisfies consumers and has a long shelf-life. Hardening and textural changes in protein bars are some of the most common modes of shelf-life failure in this product category. When the typical product creation timeline from formulation to launch can be as short as 3-6 months and with added pressure from executives to quickly launch another new product afterwards, product development scientists simply do not have time to test the full shelf life of their product before release. For this reason, it is imperative that rapid methods for detecting bar hardness and predicting shelf life of bar formulations are developed. The objective of this research is to utilize calorimetric techniques to rapidly detect and identify bar hardening reactions. Six different protein bar formulations were studied, with each containing a combination of either whey protein isolate (WPI), milk protein isolate (MPI), or partially hydrolyzed whey protein isolate (HWPI), reducing-sugar, non-reducing sugar, and vegetable shortening. All bars were stored at 45°C and ambient humidity for 21 d. Isothermal microcalorimetry (IMC) was used to evaluate bar hardening-related reactions and was compared to objective and subjective hardness measurements. Hardness, color, water activity, moisture content, and sensory evaluation were measured at d 1, 7, 14, and 21. The results of this study indicate that isothermal calorimetry may be used to narrow down bar hardening reactions and points to Maillard browning as a main driver of hardening. These techniques may be used to predict bar shelf life, if Maillard browning is used as the basis for hardening. Furthermore, this research highlights the importance of ingredient selection during bar formulation to minimize hardening.

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No. of bitstreams: 1 thallespedrosalisboa.pdf: 1465236 bytes, checksum: aaa9dd1e5c02771aa461d7ac8937e8e5 (MD5) Previous issue date: 2016-07-28 / CAPES - Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / CNPq - Conselho Nacional de Desenvolvimento Científico e Tecnológico / FAPEMIG - Fundação de Amparo à Pesquisa do Estado de Minas Gerais / Neste trabalho foi otimizado um procedimento de preparo de amostras com digestão ácida em forno de micro-ondas para a determinação do elemento mineral cromo por espectrometria de absorção atômica em forno de grafite (GF AAS) em amostras de suplemento alimentar do tipo whey protein, hipercalórico e protein bar. Os parâmetros instrumentais relativos à determinação de Cr por GF AAS foram otimizados, sendo selecionada a temperatura de pirólise de 1100 ºC para a análise das amostras de whey protein e hipercalórico e 1050 ºC para a análise das amostras de protein bar. Já a temperatura de atomização foi fixada em 2300 ºC para todas as amostras. Os valores de concentração de cromo, nas amostras, foram obtidos através de curva de calibração externa validada através da análise de variância e variaram de 0,403 a 0,647 µg/g para amostras de protein bar, 0,266 a 0,442 µg/g para amostras de hipercalórico e 0,224 a 1,04 µg/g para amostras de whey protein. Foi observada ainda a presença de cromo em amostras sem informações nutricionais rotuladas a respeito de enriquecimento dos suplementos com este micronutriente e, em alguns casos, em concentrações superiores ao indicado como dose diária recomendada para adultos, que é de 35 µg. A difração de raios X de pó (DRX) foi utilizada como ferramenta analítica para avaliação do estado de oxidação do cromo nas amostras de suplemento alimentar. Nos resultados obtidos foi verificada a presença de picos de difração característicos do Cr+3, sob a forma de picolinato de cromo, para os três tipos de amostras e a presença picos de difração característicos para o Cr+6, sob a forma de trióxido de cromo (VI), para as amostras de whey protein e hipercalórico. As determinações de sódio e potássio foram realizadas através do método de adição de padrão empregando como técnica analítica a espectrometria de emissão atômica em chama (F AES). As concentrações de Na variaram na faixa de 1,4 a 5,4 mg/g, 0,3 a 3,5 mg/g e 0,4 a 8,8 mg/g, enquanto que as concentrações de K variaram na faixa de 1,5 a 18,2 mg/g, 0,5 a 6,5 mg/g e 3,3 a 33,7 mg/g para as amostras de protein bar, hipercalórico e whey protein, respectivamente. Além disso, os resultados obtidos por F AES permitiram o cálculo da razão Na/K para as amostras de suplementos e pode-se considerá-las adequadas de acordo com as recomendações da OMS (Na/K ≤ 1). Finalmente, por meio de ensaios interlaboratoriais promoveu-se a comparação estatística dos resultados obtidos pelos métodos desenvolvidos com resultados obtidos por ICP-MS, garantindo a confiabilidade dos dados aqui apresentados. / In this work, a sample preparation procedure with acid digestion in a microwave oven has been optimized for the determination of chromium by graphite furnace atomic absorption spectrometry (GF AAS) in three types of food supplement samples: whey protein, hypercaloric and protein bar. The instrumental parameters for the determination of Cr by GF AAS have been optimized by setting the temperature pyrolysis at 1100 °C for the analysis of samples of whey protein and hypercaloric and 1050 ºC for the analysis of samples of protein bar, the atomization temperature was set at 2300 ºC for all samples. The chromium concentration values were obtained by external calibration curve, validated through variance analysis, and ranged from 0.403 to 0.647 µg/g for protein bar samples, from 0.266 to 0.442 µg/g for hypercaloric samples and from 0.224 to 1.04 µg/g for whey protein samples. It was also observed the presence of chromium in samples without nutritional information related to chromium enrichment, in which some concentrations were above the one stated as the recommended daily dose for adults (35 µg). The X-ray diffraction (XRD) was used as a chemical tool to evaluate the chromium oxidation state in the food supplement samples. The results showed the presence of characteristic diffraction peaks of Cr+3 in the form of chromium picolinate to the three types of samples and the presence of diffraction peaks characteristic to Cr+6 in the form of chromium trioxide (VI), for samples of whey protein and hypercaloric. Sodium and potassium determinations were performed by flame atomic emission spectrometry (F AES). For the analytes quantification it was used the standard addition method. The sodium concentrations varied in the range of 1.4 to 5.4 mg/g, 0.3 to 3.5 mg/g and 0.4 to 8.8 mg/g, while the potassium concentrations varied in the range of 1.5 to 18.2 mg/g 0.5 to 6.5 mg/g and 3.3 to 33.7 mg/g for the samples of protein bar, hypercaloric and whey protein, respectively. Besides, these results obtained by F AES allowed the calculation of the Na/K ratios for the supplement samples. The values obtained (≤ 1) suggest they can be considered appropriate according to WHO recommendations. Finally, through an inter-laboratory tests the results obtained by ICP-MS, showing a good agreement at a 95% confidence level. It ensured the reliability of the presented data and conclusion.