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Production and sensory analysis of yogurt with tangerine peel and pulp
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Produção e análise sensorial de iogurte com casca e polpa de tangerina
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ABSTRACT: Brazil is rich in tropical fruits with specific flavors. Searching for alternatives that
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provide a sustainable and integral use of these fruits, this study combined the yogurt to the
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pulp end peel of Murcott tangerine. The yogurt was prepared respecting the specifications of
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milk pasteurization and fermentation. The physicochemical analyses performed were: pH,
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titratable acidity, and soluble solids (ºBRIX). The final product, with samples containing
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2,84% peel and 97,16% pulp and 0% peel and 100% of pulp was subjected to sensory
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analysis, with major acceptance for the second sample, although both had shown good
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acceptance.
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KEYWORDS: Yogurt, tangerine, peel.
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RESUMO: O Brasil é rico em frutas tropicais de sabores característicos. Na busca por
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alternativas sustentáveis e que proporcionassem o aproveitamento integral dessas frutas, o
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presente trabalho combinou iogurte à polpa e casca de tangerina Murcote. O iogurte foi
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preparado respeitando às especificações da pasteurização do leite e da fermentação. As
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análises físico-químicas realizadas foram: pH, acidez total titulável, e sólidos solúveis
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(ºBrix). O produto final, com amostras contendo 2,84% de casca e 97,16% de polpa e 0% de
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casca e 100% de polpa, foi submetido a análises sensoriais, com aceitação majoritária para
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a segunda amostra, embora ambos tenham apresentado boa aceitação.
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PALAVRAS-CHAVE: Iogurte, tangerina, casca.
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1 Introduction
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Milk is one of completest food that exists. Besides calcium, it is rich in vitamins and minerals
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too. In order to increase your consumption, techniques have emerged to prepare dairy as
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cheeses, butters, condensed milks, milk drinks, yogurts, etc. There are many milk drinks
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commercially available, but according to Santos (2003), the consumers look for innovator
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products, with new textures and that bring health benefits.
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Yogurt is a kind of fermented milk, which is obtained by coagulation and decreasing of milk’s
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pH, or reconstituted through milk fermentation by the action of two specific microorganisms:
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Streptococcus thermophilus and Lactobacillus bulgaricus that act in symbiosis at
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temperatures between 42ºC to 45ºC. The fermentation consists on the transformation of
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lactose, which is a carbohydrate, in lactic acid (BRASIL, 2007).
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Mesurolle et al. (2013) point out that consumers are increasingly vigilant with regard to the
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quality of food products due to the nutritional recommendations of public authorities and
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current health issues. These authors mention that improving sensory quality of low-fat
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yogurts, for example, is a real challenge for the food industry.
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An alternative to increase the consume of yogurt, since it is usually consumed because of its
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organoleptic characteristics and not because the nutritional aspects according to Rocha et al.
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(2005), is the adding of fibers, which are found in vegetables, fruits, cereals and industrial
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wastes (e.g. peels of fruits).
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According to analysis of Gondim (2005), tangerine peel is very nutritive, rich in fibers,
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calcium and potassium. It stood out among many peels and pulp fruits cultivated in Brazil. In
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a sample of 100 g in natura of tangerine peel there are 10,38 g of fibers approximately, while
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for the same weight of the edible part there is 0,9 g. Besides the fibers, for the same mass of
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peel, there are contained about 478,98 mg of calcium, while in the pulp, this value decreases
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to 13 mg.
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Based on parameters of centesimal composition, the tangerine peel is also considered rich in
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polysaccharides, group that stands in pectin (content higher than 15%) in citric albedos in
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general. The pectin from fruits has important medicinal role, since it acts in the control of cell
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walls porosity and in an important biological surface phenomenon: the adhesion of underlying
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cells and control of the ionic ambient of the cell wall. Some types of pectin links also have
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importance on strengthen of cell wall and intercellular adherence.
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The present study aimed to use different concentrations of peel and pulp of Murcott tangerine
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for the yogurt production so as to obtain an innovator product with high nutritional value and
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toothsome.
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2 Material and Methods
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To carry out this work, murcott tangerines were commercially obtained close to Centro
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Universitário de Belo Horizonte – UniBH (Minas Gerais, Brazil), in which laboratory of
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Bromatology this research happened.
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At the beginning of the experiment, the operators led the procedures of personal hygiene,
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cleaning and sanitization of equipment, countertops and utensils, as provided in the Ordinance
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6/99 of the Health Surveillance Center, which points out the parameters and criteria for the
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hygienic-sanitary control in food establishments (BRASIL, 1999).
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2.1 Peel treatment
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Sodium hypochlorite solution 2,5% w/v, filtered water, analytical balance model QUIMIS
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Q520-4100, hot air oven with air forced circulation and renovation model DeLeo DL-AFD
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and an industrial liquefier model Skymsen LI-1,5-N were used to treat the fruits.
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The fruits were weighed, washed in running water, dipped in sodium hypochlorite solution,
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over again washed in running water, dried with a clean cloth and their peels were removed to
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separate them from the pulp. The peels were heated with filtered water in a metallic recipient.
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After three minutes of water boiling, the heat supply was interrupted and the peels were
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cooled at room temperature for four hours. The peels were after transferred to a plastic
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recipient and changes of filtered water were done every three hours during the day, and at
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night they rested at 4ºC. This procedure was repeated for four days.
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At the end of the bitterness removal procedure, the peels were again weighed and subjected to
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drying for 12 hours in a hot air oven at 60ºC and air circulation with velocity equal to 0,7 m/s.
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When dried, the peels were milled in a liquefier and sieved, so it was possible to obtain a fine
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flour of them.
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A sample of 143,86 g of peel was weighed and from the data, the water mass and the moisture
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content were calculated through the equations 1 and 2 below.
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𝑚𝑤 = 𝑚𝑝𝑤 − 𝑚𝑑
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Where mw is the mass of water, mpw is the mass of peel and water and md is the dried mass.
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𝑀% =
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Where M% represents the moisture content.
𝑚𝑤
𝑚𝑝𝑤
× 100
Eq.1
Eq. 2
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2.2 Yogurt production
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Fresh milk, which was collected in a day before the pasteurization and preparation of yogurt,
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was provided by Várzea Alegre farm, which is located in Santa Luzia/MG (Brazil).
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The milk was heated at 85ºC during 15 minutes and after cooled at 45ºC. Then, the
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microorganisms were added using the lactic culture BioRich® (to lactic fermentation occurs)
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and placed in a hot air oven to the temperature control at 43ºC for 8 h. After the fermentation,
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the yogurt was cooled at room temperature for 1 h and, next, it rested for 12 h at 5ºC.
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Two kinds of jelly were prepared: one containing peel and pulp of tangerine and the other one
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with only pulp. To prepare the jellies, it was used: filtered water, sugar, crushed pulp seed-
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free tangerine and utensils and industrial kitchen equipment.
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Under constant stirring in an industrial stove, the components were mixed to acquire jelly
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consistency. It was divided into two portions, and to one of them were added 2,84% m/m of
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peel flour.
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The product finalization was carried out mixing 20% in mass of jelly and 80% of yogurt.
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2.3 Analysis of milk and yogurt
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It was performed with milk and natural yogurt tests to determine the specific mass, using a
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picnometer and dinamic viscosity by the falling ball method described by Soares (2011). It
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was also obtained the soluble solids content using a refractometer and the lactic acid content
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by titration (BRASIL, 2006).
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So as to analyze taste, aroma, visual aspect and texture of both yogurts (with and without the
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peel), sensory analysis was performed with 57 untrained volunteers at the sensory analysis
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laboratory of Centro Universitário de Belo Horizonte – UniBH, in individual booths under
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white light and at room temperature. The samples were served in plastic cups of 50 mL.
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3 Results e Discussion
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The results of the tests, which were simultaneously done with the milk and yogurt with pulp
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and peel, are related on the TAB.1 and the standard deviation was calculated using the
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Student’s t-testst for degrees of freedom n = 3 and significance α = 0,05.
Tests
Milk
Yogurt
Specific mass (kg/m³)
1028,68 ± 0,93
994,39 ± 0,79
Viscosity (cP)
8,84 ± 0,23
556,70 ± 1,21
Soluble solids (°Brix)
12,6 ± 0,1
16,6 ± 0,3
Titratable Acidity (°Dornic)
15,5 ± 0,6
97,5 ± 0,7
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Table 1
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Results of tests with milk and yogurt
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About the ratio between mass and volume at 15ºC, the milk that was used had a result in the
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range of 1028 and 1034 g/L, which is the established by the Normative Instruction nº 51, of
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September 18th of 2002, of Ministério de Estado da Agricultura, Pecuária e Abastecimento
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(BRASIL, 2002).
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Lee and Lucey (2010) showed that the texture of yogurt and its propensity to syneresis (serum
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separation) are among the main characteristics that define yogurt’s quality. The addition of
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thickeners can be used in order to increase the product’s viscosity, making firmer the texture,
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decreasing the syneresis and increasing its acceptability.
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The viscosity value found in the product was higher than that found by Mathias et al. (2013)
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for three brands of commercial yogurts containing thickening, whose first brand had viscosity
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of 286,3 cP; the second 236,3 cP and the last one 144,7 cP.
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Thus, the yogurt produced in this research has waived the addition of thickeners, fact that
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made it more economical and has indicated its good quality.
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According to Robert (2008), the milk acidity is a fundamental parameter to the evaluation of
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its quality, because it reflects on the resistance against thermal treatment and its
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transformation in products of good quality. The milk acidity ranges from 12 to 20ºD (Dornic
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degrees), with acceptable values in the range of 15 - 18ºD. For situations out of these limits,
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this parameter indicates milk from cows milked in colostrum phase, cows with any sanitary or
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nutritional problems, with inflammatory and/or infectious processes in mammary gland.
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Compared to the results obtained for the parameter “acidity” of milk, there was compliance as
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to the established limit, which indicates the quality of milk and its derivate yogurt.
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Concerning to the parameter “soluble solids”, there was a considerable increasing if compared
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to the milk probably because of adding of pulp and peel, that have own sweet and the sugar
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adding too. The produced yogurt had value close to those found by Cavalcanti et al. (2006),
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who evaluate the characteristics of ten commercial yogurts and found average of 16,79
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ºBRIX, and lower than the seven formulations of yogurts added of fruits from Amazon
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obtained by Santa Rosa (2011), who found average of 19,41 ºBRIX.
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The sensory analysis revealed that the produced yogurt with jelly of tangerine with peel was
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well rated, considering that in all the criteria there was prevalence of answers “good” or “very
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good”, as can be seen in the Graphic 1.
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60.0%
50.0%
40.0%
Very good
Good
30.0%
Regular
Bad
20.0%
Not answered
10.0%
0.0%
Taste
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Aroma
Visual aspect
Texture
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Graphic 1
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Sensory analysis of yogurt with peel and pulp of tangerine
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The analysis of Graphic 1 in complement of Graphic 2 below allow the inference that there
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was preference for the yogurt with no addition of peel, although both had showed good
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acceptance.
60.0%
50.0%
40.0%
Very good
Good
30.0%
Regular
Bad
20.0%
Not answered
10.0%
0.0%
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Taste
Aroma
Visual aspect
Texture
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Graphic 2
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Sensory analysis of yogurt with only pulp of tangerine
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4 Conclusion
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The produced yogurt had physicochemical characteristics in accordance to the established by
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the current Brazilian Law and close to that found by other authors, which indicates its good
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quality, besides it was showed as economic mainly because of the no need of adding
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thickeners and the using of peel, that is usually discarded and whose cost is already associated
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to the value of the integral fruit.
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Both yogurts, with and without peel, had interesting sensory aspects (taste, aroma, texture,
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visual aspect) and were well rated. Although the yogurt with peel adding has greater
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nutritional value due to its higher contents of many nutrients when compared to the edible
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part, as fibers, calcium, iron, magnesium, potassium and proteins, the sample without peel in
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composition was the more preferred by tasters in the sensory analysis.
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4 Acknowledgements
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The authors of this search thank the volunteers that have collaborated in the sensory analysis
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and the workers of Pilot Plant of UniBH, who had helped with the methods and yogurt
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production.
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5 References
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