Farinhas comerciais de frutas: caracterização física, físico-química e análise de imagem digital

Abstract

The diversity of fruits produced in Brazil constitutes an alternative of consumption when industrialized in the form of flour, becoming a source of dietary bioactive compounds, fiber and minerals. They can also be used as an ingredient in the development of new, healthier and gluten-free food products. The present work aimed at the characterization, the study of chemical composition and nutritional quality of commercial fruit flour, as well as the use of digital image technology to establish a comparison their coloring patterns. Ten different samples of commercial fruit flour were collected and they were açaí (AÇ), plum (AM), green banana (BV), coconut (CO), orange (LA), lemon (LI), apple (MA), papaya (MM), passion fruit (MR) and grape (UV), and for each type of flour, three different batches were evaluated. The measurement of parameters were performed in triplicate for moisture, water activity, fixed mineral residue, proteins, dietary fiber (duplicate), pH, minerals like Cu (copper), Fe (iron), Zn (zinc), Mn (manganese), Na (sodium), K (potassium), Ca (calcium), Mg (magnesium), P (phosphorus), Co (cobalt), Cd (cadmium), Cr (chromium), Pb (cead), vitamin C content, total content of anthocyanins, antioxidant potential (DPPH, ABTS), instrumental color in color space CIE L*a*b*; CIE C*h* e XYZ. The images were obtained by digital camera and processed in software developed according to forms of programming for the study of digital imaging. Other characteristics of commercial fruit flours were derived from instrumental analytical information: X-ray diffractometry, spectroscopy in the infrared absorption region and study by thermogravimetry. The moisture content for all commercial fruit flour studied was below 15 % and the water activity (Aw) was less than 0.5000, demonstrating that the flours presented microbiological stability. The pH was variable according to the characteristics of each fruit. For the ashes content, it was observed a variation from 1.93 % ± 0.8 (MA) to 6.53 % ± 0.14 (MR). The protein content varied from 1.59 % ± 0.09 (MA) to 6.59 % ± 0.86 (MR). The highest dietary fiber content was found in the coconut commercial flour (9.40 % ±1.98). Although, it did not differ statistically from the orange commercial flour (7.63 % ± 0,81). For (LA), the Ca mineral content (412.81mg.100g-1 ±86.12) was highlighted, while (MM) presented higher K mineral content (952.11mg.100g-1 ±35.11) and Zn (2.67 mg.100g-1 ± 0.62) for (CO). Fe and P minerals (10.96 mg.100g-1 ± 3.08 and 107.06 mg.100g-1 ± 51.59, respectively) prevailed for (UV). For the analysis of vitamin C, the results found reflect its instability in the conditions of exposure to temperature and light, mainly considering that the highest content found was for (AÇ) (0.061 ± 0.01 mg.100g-1). For the DPPH methodology, the variation was of 0.035 ± 0.029 to 0.921 ± 0.063 μMTE.g-1 for (UV) and (MR), respectively and, by the ABTS methodology was of 1.135±0.257 and 12.730 ± 1.914 μM Trolox.g-1 for (CO) and (LI), respectively. Regarding the anthocyanins results, the highest value was observed for (CO) (1.132 mg.100g), which did not differ statistically from the other samples analyzed. The antioxidant content as well as the total anthocyanin content was relatively low, probably due to inadequate processing and storage conditions of such samples. The analysis of infrared absorption spectroscopy revealed similarities of functional groups (OH, C-H, C-O, C-C, C-OH, CH2 and starch) when compared to commercial fruit flours and wheat flour type 1. The X-ray diffraction analysis enabled an attempt to assign crystallinity being classified in type A the commercial flours of 8 (AÇ, AM, BV and MR); Type B the commercial flour (BV). Type C the commercial flours of (UV, MA e MM); and the flours of (MM, CO, LA and LI) were classified as type V. The thermogravimetric analysis allowed results that refer to the use of these flours under study for a production of bakery products, which can be heated above 180 °C, and the highest temperature degradation event was observed for (CO; 442 °C). Considering the resulting color characteristics for the different color channel spaces (L*, a*, b*; H, S, V; L, U, V e X, Y, Z) for each flour evaluated in this study the data showed to be of intrinsic property of the fruit that originates them, establishing a medium color system that indicated sample uniformity in the several individual each batches of flour. Also, a statistical analysis of the correlation between instrumental color comparison and the application of digital imaging technology indicated that it is possible to establish a positive correlation with the bioactive compounds, especially anthocyanins, data except for (CO). The physicochemical parameters determined in the present study were efficient in the analysis of the technical quality and nutritional profile of commercial fruit flours and demonstrated that they can be an alternative to enrich the food of the population making it healthier and more balanced.