-The acidic ninhydrin spectrophotometric method (ANSM) for quantitative determination of free and bound sialic acid of milk glycoprotein has been proved to be fast and efficient for routine detection of fraudulent addition of rennet whey to fluid milk. In this research the ANSM was compared with the high performance liquid chromatography (HPLC) method, internationally recommended for caseinomacropeptide (CMP) determination, which besides its high accuracy is more sophisticated and requires trained personnel. For several sample conditions (raw milk and milk with variable added amounts of rennet cheese whey), the methods showed an excellent linear correlation, with r = 0.981 when milk was deproteinized with a 120 g·L -1 final concentration of trichloroacetic acid (TCA) concentration. The best correlations could be seen with final concentrations of 100 g·L -1 and 80 g·L -1 TCA; respectively, r = 0.992 and 0.993. Milk / adulteration / whey / addition / acidic ninhydrin / HPLCRésumé -Détection de l'addition frauduleuse de lactosérum au lait de consommation : comparaison de la méthode à la ninhydrine acide (détermination de l'acide sialique) avec la méthode HPLC de détermination du CMP. La méthode spectrophotométrique à la ninhydrine acide (ANSM : acidic ninhydrin spectrophotometric method) pour la détermination des formes libres et liées de l'acide sialique s'est avérée être rapide et performante pour la détection en routine de l'addition frauduleuse de lactosérum doux dans le lait de consommation. Dans l'étude réalisée, l'ANSM a été comparée avec la méthode recommandée au niveau international, à savoir la méthode de détermination du caséinomacropeptide (CMP) par HPLC qui est certes très précise mais requiert un équipement sophistiqué et du personnel hautement qualifié. Une excellente corrélation linéaire a été trouvée entre les deux méthodes lors de l'analyse de filtrats TCA (acide trichloroacétique) issus d'échantillons de lait cru additionnés de quantités variables de lactosérum doux soumis préalable-ment à un traitement thermique. Selon la concentration finale en TCA : 120 g·L -1 , 100 g·L -1 , 80 g·L -1 , les valeurs de corrélation linéaire atteignaient respectivement 0,981, 0,992 et 0,993.Lait / fraude / lactosérum / addition / ninhydrine acide / HPLC * Corresponding author: salvador@fea.unicamp.br 502 S.P. Fukuda et al.
The possibility of the survival, germination, and multiplication of Bacillus cereus in extended-shelf-life milk prompted research into the occurrence of the bacteria in refrigerated milk submitted to different heat treatments. Samples were submitted to ultrapasteurization (138 degrees C for 2 s), "superpasteurization" (96 degrees C for 13 s), and pasteurization (74 degrees C for 15 s) and stored under refrigeration at 4 +/- 2 degrees C for up to 6 weeks. The milk was analyzed for its sensory quality and for the quantitative determination of mesophilic and psychrotrophic B. cereus in the vegetative form at incubation temperatures of 7 and 30 degrees C, in addition to standard plate counts and psychrotrophic counts. In the three experimental trials, the psychrotrophic B. cereus counts were below the detection limit of the methodology (<10 CFU/ml) in all of the samples analyzed, independent of the heat treatment and storage period. The count of mesophilic B. cereus was restricted to samples of superpasteurized and pasteurized milk from a single trial, reaching 4.0 x 10(1) and 7.0 x 10(5) CFU/ml, respectively. Although the pasteurized milk had higher populations of mesophilic B. cereus after the second week of storage, flavor defects resulting in sensory rejection of the product did not appear before the fourth week of storage. The results of this research indicate that superpasteurization and ultrapasteurization are adequate for maintaining the product at refrigeration temperatures for 6 weeks. Pasteurized milk produced under clean conditions should have a shelf life limited to less than 2 weeks.
Proteólise e derretimento do queijo prato obtido por ultrafiltração, Roig et al.
-INTRODUÇÃOA Mussarela é o queijo de massa filada mais produzido no Brasil e segundo estimativas de FURTADO [9] sua produção deve superar 200 mil toneladas. Este tipo de queijo é utilizado principalmente no preparo de pizzas devendo apresentar boas propriedades funcionais de fatiamento, derretimento, liberação de óleo livre, estiramento, escurecimento não enzímico e formação de blisters [17]. Pesquisas realizadas em pizzarias indicaram que entre as críticas mais freqüentes feitas pelos consumidores ao queijo Mussarela usado nas pizzas, encontram-se: derretimento excessivo do queijo e a formação de blisters [26].Além do processo tradicional, há relatos de fabricação de queijo Mussarela por ultrafiltração desde o final dos anos 70 [5,22]. A ultrafiltração consiste numa tecnologia utilizada para concentrar o leite por meio de membranas semipermeáveis [6]. A elaboração de queijo Mussarela, a partir de retentado com teor de sólidos semelhante ao do queijo obtido pelo processo tradicional (concentração total), tende a apresentar inúmeras vantagens, tais como: economia no tratamento de efluentes, melhor utilização do espaço físico da fábrica e aumento de rendimento de fabricação dos queijos [18,20,23,24]. Porém, tal queijo pode apresentar problemas de filagem, bem como menores valores de derretimento e estiramento [5,18,21], uma vez que tende a apresentar em sua composição as soroproteínas, as quais afetam a proteólise [21], que é um dos principais fatores que influenciam tais propriedades funcionais [16]. Uma alternativa para conciliar as vantagens da técnica de ultrafiltração do leite com uma redução nas desvantagens que ela apresenta seria fabricar queijo Mussarela a partir de retentado de FCV intermediário (FCV 4:1 a 6:1), obtendo desta forma queijos com características mais próximas das de um queijo Mussarela tradicional.No presente estudo queijos tipo Mussarela fabricados a partir de retentado (FCV=2,34:1) e pelo processo tradicional (leite não ultrafiltrado) foram analisados e comparados com relação a: composição, proteólise, capacidade de derretimento e formação de blisters . -MATERIAL E MÉTODOS -Ultrafiltração do leiteLeite cru tipo B (100kg), proveniente da Cooperativa dos Produtores de Leite da Região de Campinas, foi tratado termicamente a 68°C/2min. Uma parte do leite (20kg) foi resfriada a 35°C e colocada em uma cuba de fabricação (capacidade para 20kg) para elaboração de It was realized one production assay with 3 batches of MRs and one of MP. It was evaluated the milk, retentate, whey, stretching water and cheeses composition and the proteolysis, melting capacity and the blisters formation on cheeses with 7, 15, 30 and 60 days of refrigerates storage. MRs presented larger pH, ash and total protein contents and lower titratable acidity and fat, fat on dry matter and salt contents when compared to MP. Along the storage time the MRs presented lower proteolysis and melting capacity in all the analyzed dates. The pizza area percentage covered by blisters and their average diameters were larger for the MP dur...
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