Microfiltration and ultra-high-pressure homogenization for extending the shelf-storage stability of UHT milk

Fat separation, gelation or sedimentation of UHT milk during shelf-storage represent instability phenomena causing the product rejection by consumers. Stability of UHT milk is of increasing concern because access to emerging markets currently implies for this product to be stable during shipping and prolonged storage, up to 12 months. The role of microfiltration prior to UHT process in avoiding or retarding the gelation or sediment formation was studied by comparing microfiltered UHT milk to conventional UHT milk. A second trial was set up to study the effects of double ultra-high pressure homogenization in delaying the cream rising and UHT milk homogenized once at lower pressure was taken as control. All milk samples were produced at industrial plant level. Milk packages were stored at 22 \ub0C, opened monthly for visually inspecting the presence of cream layer, gel or sediment and then analysed. Microfiltration markedly delayed the formation of both gel particles and sediment, with respect to the control, and slowed down the proteolysis in terms of accumulation of peptides although no correlation was observed between the two phenomena. The double homogenization, also evaluated at ultra-structural level, narrowed the fat globule distribution and the second one (400 MPa), performed downstream to the sterilization step, disrupted the fat-protein aggregates produced in the first one (250 MPa). The adopted conditions avoided the appearance of the cream layer in the UHT milk up to 18 months. This study contributes important knowledge for developing strategies to delay instability phenomena in UHT milk destined to extremely long shelf storage

Changes in the soluble nitrogen fraction of milk throughout PDO Grana Padano cheese-making

The behaviour of soluble nitrogen compounds during Grana Padano cheese-making was studied at eight dairies. Raw milk, skimmed milk, sweet whey and the derived natural whey culture, collected from 24 processes, were analysed for soluble whey proteins (\u3b1-lactalbumin and \u3b2-lactoglobulin), proteose-peptones (PP), small peptides (SP), caseinomacropeptides (CMPs), and free amino acids (FAAs). The PP fraction increased during milk natural creaming, then part of it was selectively retained in the curd and the rest degraded in the first few hours of whey fermentation, together with \u3b1-lactalbumin, CMPs and part of SP. Features outlined for the whey culture were confirmed on 30 samples collected at six different dairies. A time course study of the whey fermentation showed that degradation of \u3b1-lactalbumin began when the pH dropped below 4, whereas \u3b2-lactoglobulin content did not change. Uptake of specific FAAs was shown to support the initial growth of lactic acid bacteria in whey

Ion-Exchange Chromatographic Method for the Determination of the Free Amino Acid Composition of Cheese and Other Dairy Products : an Inter-Laboratory Validation Study

Although free amino acids (FAAs) represent a significant component of ripened cheeses and can provide useful information for their characterization, no inter-laboratory validated analytical method exists which allows a reliable comparison of data obtained by different laboratories and the adoption of quality control schemes based on FAA pattern. The objective of the present work was to test the effectiveness of an analytical protocol for the determination of the FAA composition of cheese and to verify the adequateness of this type of analysis for quality control procedures of Grana Padano PDO cheese as well as for research purposes. After an initial test to compare performances of ion-exchange chromatography (IEC) and HPLC techniques, an inter-laboratory collaborative study (seven laboratories, four samples) was organized to validate an IEC method with post-column ninhydrin derivatization and using l-norleucine as an internal standard. Determined amounts of individual FAA ranged from 8 to over 1380 mg/100 g cheese, with relative standard deviation of repeatability (RSDr) ranging from 0.5 to 4.6%, and relative standard deviation of reproducibility (RSDR) ranging from 1.3 to 9.9% for FAA concentrations over 100 mg/100 g. For lower concentrations, RSDr and RSDR were about thrice as high. On the basis of the results of this investigation, at present, the validated method is adopted as the official method for the determination of FAA patterns in the quality control of Grana Padano PDO cheese

Macromolecular Traits in the African Rice Oryza glaberrima and in Glaberrima/Sativa Crosses, and Their Relevance to Processing

Molecular properties of proteins and starch were investigated in 2 accessions of Oryza glaberrima and Oryza sativa, and in one NERICA cross between the 2 species, to assess traits that could be relevant to transformation into specific foods. Protein nature and organization in O. glaberrima were different from those in O. sativa and in NERICA. Despite the similar cysteine content in all samples, thiol accessibility in O. glaberrima proteins was higher than in NERICA or in O. sativa. Inter-protein disulphide bonds were important for the formation of protein aggregates in O. glaberrima, whereas non-covalent protein-protein interactions were relevant in NERICA and O. sativa. DSC and NMR studies indicated only minor differences in the structure of starch in these species, as also made evident by their microstructural features. Nevertheless, starch gelatinization in O. glaberrima was very different from what was observed in O. sativa and NERICA. The content of soluble species in gelatinized starch from the various species in the presence/absence of treatments with specific enzymes indicated that release of small starch breakdown products was lowest in O. glaberrima, in particular from the amylopectin component. These findings may explain the low glycemic index of O. glaberrima, and provide a rationale for extending the use of O. glaberrima in the production of specific rice-based products, thus improving the economic value and the market appeal of African crops

Lysozyme side effects in Grana Padano PDO cheese: new perspective after 30 years using

Since thirty years, hen\u2019s egg white lysozyme is in use as an anti-clostridial agent in Grana Padano PDO cheese manufacturing in order to avoid the cheese blowing defect. However, as the EU legislation includes egg among allergens, Grana Padano falls into the category of food products containing allergens. In view of discontinuing this situation, this work aimed to investigate the effects of abandoning lysozyme use on cheese characteristics. Nine manufacturing processes, conducted with and without lysozyme, were monitored from milk to ripened cheese at four different dairies. Both the lactic acid bacteria microbiota (LAB) and chemical parameters related to cheese maturation were evaluated. The presence of the enzyme seems to affect the capacity of some LAB species and biotypes to grow in cheese during ripening. Accordingly, primary proteolysis was not affected, whereas differences were found in amino acids release that could be traced back to the lysozyme-dependent LAB growth

Proteolytic Activity and Production of γ-Aminobutyric Acid by Streptococcus thermophilus Cultivated in Microfiltered Pasteurized Milk

A set of 191 strains of Streptococcus thermophilus were preliminarily screened for the presence of the genes codifying for cell envelope-associated proteinase (prtS) and for glutamate decarboxylase (gadB) responsible for \u3b3-aminobutyric acid (GABA) production. The growth and proteolytic activity of the gadB-positive strains (9 presenting the prtS gene and 11 lacking it) were studied in microfiltered pasteurized milk. Degradation of both caseins (capillary electrophoresis) and soluble nitrogen fractions (HPLC) and changes in the profile of free amino acids (FAAs; ion-exchange chromatography) were evaluated at inoculation and after 6 and 24 h of incubation at 41 \ub0C. None of the strains was capable of hydrolyzing caseins and \u3b2-lactoglobulin, and only two hydrolyzed part of \u3b1-lactalbumin, these proteins being present in their native states in pasteurized milk. Contrarily, most strains were able to hydrolyze peptones and peptides. For initial growth, most strains relied on the FAAs present in milk, whereas, after 6 h, prtS+ strains released variable amounts of FAA. One prtS+ strain expressed a PrtS- phenotype, and two prtS- strains showed a rather intense proteolytic activity. Only five strains (all prtS+) produced GABA, in variable quantities (up to 100 mg/L) and at different rates, depending on the acidification strength. Addition of glutamate did not induce production of GABA in nonproducing strains that, however, unexpectedly were shown to adopt the degradation of arginine into citrulline and ornithine as an alternative acid resistance system and likely as a source of ATP

Gli amminoacidi liberi nella tipizzazione del formaggio Parmigiano-Reggiano ed in particolare del prodotto grattugiato

La determinazione degli amminoacidi (aa) liberi, mediante HPLC, si prospetta come un valido mezzo per tipizzare il formaggio Parmigiano-Reggiano (P.R.) anche allo stato grattugiato. Determinazioni condotte su oltre 70 campioni di formaggio, di cui 44 di P.R. tipico con et\ue0 compresa fra 2 e 24 mesi, hanno permesso di riconoscere un preciso andamento nell\u2019accumulo degli aa liberi nel corso della stagionatura. Esso \ue8 rappresentabile sia da una curva di regressione ad elevata significativit\ue0 statistica (r2=0.954) che correla contenuto totale in aa liberi ed et\ue0; sia da una serie di rette di regressione ((r2>0.85) che correlano il contenuto in singoli aa liberi con l\u2019et\ue0, nel periodo di stagionatura 0-15 mesi. In ogni caso tali regressioni permettono di risalire con buona approssimazione (\uf0b120% dell\u2019et\ue0 determinata) all\u2019et\ue0 del P.R. noto il suo pattern amminoacidico. Risulta altres\uec possibile controllare la tipicit\ue0 di un formaggio, anche allo stato grattugiato e definito P.R., sulla base dello scostamento del suo pattern amminoacidico da quello tipico del P.R. all\u2019et\ue0 determinata; sia di indicare valori soglia per alcuni aa liberi ( espressi in % relative) che permettono, fra l\u2019altro, di accertare la presenza di formaggio di scadente qualit\ue0 (basso valore di istidine e/o alto valore di acido gamma-ammino-butirrico) e di crosta non pertinente (alto valore di metionina). Controlli eseguiti in questo senso su formaggi grattugiati del commercio, commercializzati in Europa e definiti P.R., mostrano come raramente questi prodotti siano ascrivibili al nostro formaggio tipico di qualit\ue0 accettabile.The possibility to characterize Parmigiano-Reggiano cheese (P.R.) by determining the free amino acids (aa) and statistically evaluating the data has been investigated. The analyses have been carried out by reversed-phase HPLC on C18 column with OPA precolumn derivatization and fluorescence detection. Over 70 samples including typical P.R. aged between 2 and 24 months (44 samples), commercial cheeses and grated products were analyzed. The content of free aa of P.R. samples with the same ripening period looks highly constant for the typical cheese manufactured in different dairies of the area under control of the \u201cConsorzio del Parmigiano-Reggiano\u201d. As ripening proceeds the uniformity for free aa composition becomes higher. Therefore it is possible for P.R. to point out either a non-linear regression function which correlates, with high statistical significance (r2=0.954), total free aa content with cheese age; or a set of linear regressions (r2>0.85) which correlate single free aa content with cheese age in the first 15 ripening months. According to our experimental data, reported in 15 tables and 10 statistical graphs and discussed in detail for the involved aspects of biochemistry of cheese ripening, it is likely possible: \u2022 to state a minimum level of total free aa content (as percentage of total cheese protein) which corresponds, with a chose significance level (e.g. 2 \u3c3), to the age stated as minimum for selling P.R.; \u2022 to determine the age of P.R. until 12 ripening months, with a confidence interval lower than 20% of the calculated value, at a significance level higher than 95%; \u2022 to evaluate the age of longer ripened (15-24 months) P.R. on the basis of the relative percentages of serine, glutamine, alanine (i.e. values calculated on the total free aa content); \u2022 to control if a cheese, labeled as P.R. or similarly named, is a typical one, calculating the shifting of its free aa pattern from the pattern of typical P.R. at the determined age; \u2022 to state for some free aa threshold levels (t.l.), calculated as relative percentages, which allow to distinguish typical P.R. from similar cheeses (t.l. for alanine, glycine, serine, glutamine); to indicate poor quality of cheese (t.l. for histidine and gamma amino butyric acid); to find out addition of grated rind in the grated products (t.l. for methionine). Many of the commercial products sold in Europe as well as prepacked slices always labeled as Italian Parmesan cheese or P.R. type, controlled according to the above mentioned analytical parameters, show poor quality, too short ripening periods or don\u2019t seem to be typical P.R

La caratterizzazione analitica del formaggio Fontina sulla base della sua composizione in amminoacidi liberi

La composizione in amminoacidi liberi del formaggio Fontina \ue8 stata studiata su 80 campioni di origine nota e rappresentativi delle diverse condizioni produttive (zona e periodo di produzione, caseificio, durata della stagionatura), nonch\ue9 su 21 campioni reperiti in commercio. La possibilit\ue0 di differenziare questo formaggio da prodotti similari sulla base di parametri oggettivi \ue8 stata valutata analizzando anche 24 campioni di formaggio Fontal di diversa origine. L\u2019elaborazione statistica dei dati ha consentito di individuare nel rapporto (GLN+TYR)/(ILE+LYS+GABA) un parametro analitico capace di differenziare (P<0.01) il formaggio Fontina dal Fontal a qualunque stadio di stagionatura. Viene inoltre evidenziato il ruolo chiave della microflora nativa del late nel determinare le caratteristiche di tipicit\ue0 della Fontina