Vera Lúcia Valente-Mesquita

Pressure-Induced Subunit Dissociation and Unfolding of Dimeric β-Lactoglobulin

Effects of hydrostatic pressure on dimeric beta-lactoglobulin A (beta-Lg) were investigated. Application of pressures of up to 3.5 kbar induced a significant red shift ( approximately 11 nm) and a 60% increase in intrinsic fluorescence emission of beta-Lg. These changes were very similar to those induced by guanidine hydrochloride, which caused subunit dissociation and unfolding of beta-Lg. A large hysteresis in the recovery of fluorescence parameters was observed upon decompression of beta-Lg. Pressure-induced dissociation and unfolding were not fully reversible, because of the formation of a nonnative intersubunit disulfide bond that hampered correct refolding of the dimer. Comparison between pressure dissociation/unfolding at 3 degrees C and 23 degrees C revealed a marked destabilization of beta-Lg at low temperature. The stability of beta-Lg toward pressure was significantly enhanced by 1 M NaCl, but not by glycerol (up to 20% v/v). These observations suggest that salt stabilization was not related to a general cosolvent effect, but may reflect charge screening. Interestingly, pressure-induced dissociation/unfolding was completely independent of beta-Lg concentration, in apparent violation of the law of mass action. Possible causes for this anomalous behavior are discussed.

Effect of high hydrostatic pressure on phenolic compounds, ascorbic acid and antioxidant activity in cashew apple juice

The cashew apple is native to Brazil, but there is insufficient information regarding the nutritional properties of this fruit. The objective of this study was to evaluate the impact of high pressure processing (HPP) at room temperature (25 °C) on phenolic compound and ascorbic acid contents and antioxidant capacity of cashew apple juice. This study showed that HPP at 250 or 400 MPa for 3, 5 and 7 min did not change pH, acidity, total soluble solids, ascorbic acid or hydrolysable polyphenol contents. However, juice pressurized for 3 and 5 min showed higher soluble polyphenol contents. Antioxidant capacity, measured by the ferric-reducing antioxidant power method, was not altered by HPP, but when treated at 250 MPa for 3 min, it resulted in an increased value when 2,2-diphenyl-1-picrylhydrazyl was used. These data demonstrate that HPP can be used in the food industry for the generation of products with higher nutritional quality.

Sucos de laranja industrializados e preparados sólidos para refrescos: estabilidade química e físico-química

Fresh orange juice is considered to be one of the best sources of vitamin C. Nevertheless, hand squeezed juice is often inconvenient for consumers who seek practical and fast ways to prepare their meals. The objective of this study was to analyze the chemical and physicochemical stability of ready to drink and refreshments prepared from orange juice powder commercially available in the city of Rio de Janeiro. The ascorbic acid (AA) content, total soluble solids (TSS), total tritatable acidity (TAA) and pH were determined. The AA content of ready to drink orange juice ranged from 17.25mg% to 62.40mg (p = 0.05). In two batches the AA content was lower than that established by the Brazilian legislation. The AA content of refreshments prepared from orange juice powder ranged from 0.67mg% to 32.00mg% among samples (p = 0.05). TSS and pH values were stable, while TTA changed during the storage time. Industrialized ready to drink orange juices may be considered a source of vitamin C, whereas most of the cheaper refreshments prepared from powder orange juice are not.

Estudo da estabilidade quÍmica e microbiológica do suco de caju in natura armazenado em diferentes condições de estocagem

O caju, rico em nutrientes, apresenta alta perecibilidade. Este trabalho teve como objetivo avaliar a estabilidade quimica, fisico-quimica e microbiologica do suco de caju in natura mantido em temperatura ambiente por 24 h, estocado sob refrigeracao por sete dias e sob congelamento por 120 dias. O teor de acido ascorbico no suco recem-extraido foi de 147,29 ± 0,41 mg/100 mL e reduziu em 6,57% em temperatura ambiente. Durante a estocagem sob refrigeracao e congelamento, as taxas de reducao dessa vitamina foram 1,16% ao dia e 0,05% ao dia, respectivamente. Foi observado aumento na contagem de bacterias mesofilas totais e fungos filamentosos e leveduras no suco mantido em temperatura ambiente. Nos sucos estocados sob refrigeracao durante sete dias houve reducao da contagem de bacterias mesofilas totais e aumento na contagem de fungos filamentosos e leveduras. Nos sucos congelados, a contagem de fungos filamentosos e leveduras permaneceu inferior a inicial, enquanto a de bacterias mesofilas totais apresentou variacao ate o trigesimo dia. A partir deste periodo, esta permaneceu estavel em menos de um ciclo logaritmico acima da contagem inicial. Nos periodos estudados, refrigeracao e congelamento mostraram-se eficazes na preservacao do acido ascorbico e da qualidade microbiologica do suco de caju in natura.

Proximate and mineral composition of industrialized biscuits

Abstract The aim of this study was to analyze the proximate and mineral composition of 21 types of biscuits. All biscuits showed high fat contents, significantly different ( P < 0.05) from those described on the labels, except for three brands. Insoluble fiber fractions were predominant in the analyzed samples. Among the 21 biscuits analyzed, 16 showed food label values 20% higher than those allowed by law, according to RDC 360, for fat, protein, total fiber, calcium, and sodium levels. This difference reached 273% for the sodium content. The calcium content was included only on the label of three samples analyzed, and the values described were significantly lower than those obtained analytically. Considering that biscuits are consumed by people of all age groups and of different socioeconomic levels, the results can contribute to the plans for health policies, such as surveillance of nutritional labeling, ensuring the reliability of the information provided by the food industry and enabling the identification of the relationship between dietary factors and the occurrence of non-transmissible chronic diseases.

Impacto da estocagem sobre atividade antioxidante e teor de ácido ascórbico em sucos e refrescos de tangerina

OBJECTIVE: The objective of this study was to analyze the ascorbic acid stability of mandarin juice from the cultivar Ponkan under different storage conditions, and of 13 samples of processed mandarin beverages, as well as the antioxidant activity stability of fresh juice. METHODS: Fresh mandarin juice was stored under three temperatures: room temperature, refrigeration and freezing. Mandarin samples were kept under refrigeration. Thirteen brands of processed mandarin beverages were purchased and kept under refrigeration. Ascorbic acid level was determined by the Tillmans titrimetric method (Association of Official Analytical Chemists) and antioxidant activity by the radical scavenger capacity using the 2,2-diphenyl-1-picrylhydrazyl radical. RESULTS: The mean ascorbic acid level in fresh juice was 32.40mg/100mL and the reduction rate of this nutrient was higher when the samples were stored under higher temperatures. The average antioxidant activity was 89.74% of 2,2-diphenyl-1-picrylhydrazyl radical inhibition, with variations of up to 4.26% during storage. Among the processed beverages, the mean ascorbic acid content varied from 1.01 to 10.72mg/100mL, with losses of up to 82.76%. Six brands of processed beverages were considered noncompliant with the Brazilian legislation regarding the ascorbic acid content reported in the labels. CONCLUSION: Mandarin juice from the Ponkan cultivar has high antioxidant activity, even during storage. The fresh juice was nutritionally better than the processed beverages, considering ascorbic acid content and stability. Additionally, the results indicated the need of greater surveillance of nutritional labeling.