Volatilome of chill-stored European Seabass (Dicentrarchus labrax) fillets and Atlantic Salmon (Salmo salar) slices under modified atmosphere packaging

Fish spoilage occurs due to production of metabolites during storage, from bacterial action and chemical reactions, which leads to sensory rejection. Investigating the volatilome profile can reveal the potential spoilage markers. The evolution of volatile organic molecules during storage of European seabass (Dicentrarchus labrax) fillets and Atlantic salmon (Salmo salar) slices under modified atmosphere packaging at 2 °C was recorded by solid-phase microextraction combined with gas chromatography-mass spectrometry. Total volatile basic nitrogen (TVB-N), microbiological, and sensory changes were also monitored. The shelf life of seabass fillets and salmon slices was 10.5 days. Pseudomonas and H2S-producing bacteria were the dominant microorganisms in both fish. TVB-N increased from the middle of storage, but never reached concentrations higher than the regulatory limit of 30–35 mg N/100 g. The volatilome consisted of a number of aldehydes, ketones, alcohols and esters, common to both fish species. However, different evolution patterns were observed, indicating the effect of fish substrate on microbial growth and eventually the generation of volatiles. The compounds 3-hydroxy-2-butanone, 2,3-butanediol, 2,3-butanedione and acetic acid could be proposed as potential spoilage markers. The identification and quantification of the volatilities of specific fish species via the development of a database with the fingerprint of fish species stored under certain storage conditions can help towards rapid spoilage assessment

Extraction of Phenolic Compounds from Palm Oil Processing Residues and Their Application as Antioxidants

Nusproizvodi proizvodnje palminog ulja, i to pogača od palminih sjemenki, palmina vlakna, ljuske palminih sjemenki i prazni grozdovi palminog ploda, upotrijebljeni su za ekstrakciju polifenolnih spojeva. Među tim nusproizvodima je pogača od palminih sjemenki sadržavala najviše ukupnih fenolnih spojeva, i to 5,19 mg u g suhe tvari, izraženih kao ekvivalent galne kiseline, dok je najmanje imao prazni grozd palminog ploda, i to 1,79 mg/g. Radi optimiranja ekstrakcije fenola ispitani su sljedeći parametri: vrijeme ekstrakcije i omjer tekuće i krute tvari. Najveći ukupni udjel fenola od 5,35 mg/g pri omjeru tekuće i krute tvari od 40:1 tijekom ekstrakcije od 20 min imala je pogača od palminih sjemenki. Pomoću HPLC-DAD metode određeni su glavni fenolni spojevi iz nusprodukata proizvodnje palminog ulja. Pogača od palminih sjemenki sadržavala je najviše pirogalola, te 4-hidroksibenzojeve, galne i ferulinske kiseline. Prazni grozdovi palminog ploda i palmina vlakna bili su bogati hidroksibenzojevom kiselinom, dok je pirogalol bio dominantan sastojak ekstrakta ljuski palminih sjemenki. Svi su ekstrakti imali oksidacijsku aktivnost, koja je potvrđena DPPH analizom, te ispitana dodatkom ekstrakta suncokretovom ulju radi produljenja roka trajanja. Dodatkom 0,8 % ekstrakta pogače od palminih sjemenki povećalo se indukcijsko vrijeme suncokretovog ulja za više od 50 %. Rezultati istraživanja potvrđuju da je pogača od palminih sjemenki nusproizvod s dodanom vrijednošću koji se može upotrijebiti kao antioksidans u prehrambenoj industriji.The side streams derived from the palm oil production process, namely palm kernel cake, palm pressed fibre, palm kernel shells and empty fruit bunches, were evaluated as sources of phenolic compounds. Among these streams, kernel cake had the highest total phenolic content (in mg of gallic acid equivalents (GAE) per g of dry sample) with a value of 5.19, whereas the empty fruit bunches had the lowest value (1.79). The extraction time and liquid-to-solid ratio were investigated to optimize the phenolic extraction. Kernel cake exhibited the highest total phenolic content (5.35 mg/g) with a liquid-to-solid ratio of 40:1 during 20 min of extraction. The main phenolic compounds of the extracts deriving from all byproduct streams were also identified and quantified with HPLC-DAD. Pyrogallol, 4-hydroxybenzoic acid, gallic acid and ferulic acid were the main compounds found in kernel cake extracts. Empty fruit bunch and pressed fibre extracts were also rich in 4-hydroxybenzoic acid, while pyrogallol was the predominant compound in kernel shell extracts. All extracts showed antioxidant activity as it was indicated from the results of DPPH analysis and subsequently tested in sunflower oil aiming to prolong its shelf life. The addition of 0.8 % kernel cake extract increased the induction time of sunflower oil more than 50 %. According to the results obtained in this study, kernel cake extracts could be considered as a value-added co-product with a potential application as antioxidants in the food industry

Study of secondary aroma by GS/MS of wines produced by immobilized cells

Repeated batch fermentations of grape must at different temperatures were performed using immobilized cells of Saccharomyces cerevisiae strain AXAZ-1 on delignified cellulosic material (DCM), gluten pellets (GP) and grape skins. The aim of this study was the investigation of the volatile components of the final product (qualitatively and quantitatively) as well as the monitoring of the evolution of some volatiles during the alcoholic fermentation. For comparison reasons, fermentations using free cells were performed under the same conditions. The immobilized biocatalyst on DCM and GP resulted in significant increase of the fermentation rate in comparison with free cells. The produced wines had similar physicochemical characteristics, e.g. alcoholic strength, total and volatile acidity, residual sugar and pH. The GC/MS analysis proved that the cell immobilization and the fermentation temperature did not cause serious changes in the qualitative composition of the wine aroma. Esters, higher alcohols and volatile fatty acids were the major compounds identified in all wines. However, the effect of immobilization and temperature caused signigicant changes on the quantitative profile of the wine aroma. Wines produced by DCM contained higher amounts of esters, at every temperature. The relative percentage of esters on total volatiles remained practically constant with temperature decrease, in the case of immobilized cells, whereas it decreased in the case of free cells. Wines produced by GP-supported biocatalyst contained higher amounts of alcohols. DCM-supported biocatalyst and free cells produced wines with similar contents of alcohols. The decrease of temperature resulted in the decrease of their amount. The same was observed for the concentration of volatile fatty acids. GPsupported biocatalyst produced wines with smaller amounts of acids. Free and immobilized cells on DCM produced wines with similar contents of volatile acids. The kinetics of volatiles’ production were similar for free and immobilized cells on DCM. In all cases, immobilized cells showed a higher rate of volatile production. This was directly connected to sugar consumption. The evolution patterns of acetate esters were different from those of ethyl esters. Generally, ethyl esters reached a maximum earlier than acetates. In most cases, a two-peak profile was observed for ethyl esters. For the first time, grape skins were used as a natural support for S. cerevisiae immobilization. Cell immobilization was confirmed by electron microscopy. In repeated batch fermentations of grape must, the immobilized biocatalyst caused an significant increase in the fermentation rate in comparison with free cells, without any loss of the activity, even at very low temperatures (5oC). The alcohol production and the maximum specific rates on glucose and fructose substrate were much better for cells immobilized on grape skins. They increased exponentially with temperature increase. Qualitative characteristics, such as total acidity, volatile acidity and residual sugars were similar with those of commercial dry wines. Wines produced by immobilized cells had lower volatile acidity than those produced by free cells. They were very clear, especially at low fermentation temperatures. GC/MS analysis showed that the qualitative profile of the produced wines was similar in all cases. The majority of the identified volatile compounds was formed during the alcoholic fermentation and consisted of esters, alcohols and acids. Immobilized cells gave wines with a higher content of esters. The amount of ethyl esters decreased with temperature decrease, whereas the amount of acetate esters increased with temperature decrease (25-15oC), reaching a maximum. The content of volatile alcohols was more pronounced in wines produced by free cells. It decreased dramatically at low fermentation temperatures (10oC). Volatile fatty acids were produced in greater quantities by free cells at higher temperatures (25-20oC). The opposite was observed at low fermentation temperatures (15-10oC). Investigation of the volatiles’ evolution during fermentation, showed that esters were produced shortly after the midpoint of fermentation. For immobilized cells, the formation of esters was continued until the end of the process. Similar kinetics were observed for amyl alcohols and 2-phenylethanol, whereas propanol and isobutanol were formed during the whole alcoholic fermentation period with a constant rate. Acetaldehyde and acetoin were synthesized in the early stages. Afterwards, their amount decreased. Acetic acid was formed throughout alcoholic fermentation with a costant rate, which was greater in the case of free cells at every temperature studied

Gas Chromatography–Mass Spectrometry-Based Metabolite Profiling for the Assessment of Freshness in Gilthead Sea Bream (Sparus aurata)

Gilthead sea bream (Sparus aurata) is one of the most important farmed Mediterranean fish species, and there is considerable interest for the development of suitable methods to assess its freshness. In the present work, gas chromatography–mass spectrometry-based metabolomics was employed to monitor the hydrophilic metabolites of sea bream during storage on ice for 19 days. Additionally, the quality changes were evaluated using two conventional methods: sensory evaluation according to European Union’s grading scheme and K-value, the most widely used chemical index of fish spoilage. With the application of chemometrics, the fish samples were successfully classified in the freshness categories, and a partial least squares regression model was built to predict K-value. A list of differential metabolites were found, which were distinguished according to their evolution profile as potential biomarkers of freshness and spoilage. Therefore, the results support the suitability of the proposed methodology to gain information on seafood quality

Assessment of Volatile Compounds Evolution, Antioxidant Activity, and Total Phenolics Content during Cold Storage of Pomegranate Beverage Fermented by <i>Lactobacillus paracasei</i> K5

A recently isolate from feta type cheese, potential probiotic strain Lactobacillus paracasei K5, was applied for pomegranate juice (Punica granutum L.) fermentation. Fermentations were carried out for 24 h followed by the storage of pomegranate juices at 4 &#176;C for 4 weeks. The parameters examined were a composition of volatile compounds, antioxidant activity, total phenolic content, and consumers&#8217; acceptance. The results were encouraging showing that lactic acid fermentation enhanced the composition of volatile compounds even at the fourth week of storage. Increased antioxidant activity (151.44 mg TE/100 mL at the second week) and total phenolics content (285 mg GAE/100 mL at the third week) were observed for all the storage times compared to the initial pomegranate beverage. The fermented pomegranate beverage received better scores for the last 3 weeks of cold storage compared to the non-fermented one. Likewise, L. paracasei K5 was proved to be suitable for the production of functional pomegranate beverages with enhanced aromatic characteristics and high nutritional value

Vinegar Production from Corinthian Currants Finishing Side-Stream: Development and Comparison of Methods Based on Immobilized Acetic Acid Bacteria

Fruit wastes and side-streams can be used for vinegar production to create added value for the agri-food sector and enhance farmer incomes and local economies. In this study, methods for vinegar production by wild and selected acetic acid bacteria (the quick starter Acetobacter aceti and the acid-resistant Komagataeibacter europaeus), free (FC) and immobilized (IC) on a natural cellulosic carrier, are proposed using sweet wine made from the industrial finishing side-stream (FSS) of Corinthian currants as raw material. The results showed all cultures can produce vinegar with 46.65 &plusmn; 5.43 g/L acidity, from sweet FSS wine containing 5.08 &plusmn; 1.19% alcohol. The effect of immobilization was more obvious in the case of the selected culture, presenting better acetification efficiency, both fresh and after cold storage for 2 months. The vinegars had an antioxidant capacity of 263.5 &plusmn; 8.4 and 277.1 &plusmn; 6.7 mg/L (as ascorbic acid) and phenolic content 333.1 &plusmn; 12.0 and 222.2 &plusmn; 2.9 mg/L (as gallic acid) (for FC and IC, respectively). They also had a rich volatilome (140 compounds identified by SPME GC-MS), with higher percentages of esters identified in vinegars made by IC. The results are encouraging for vinegar production with IC of a mixed A. aceti and K. europaeus culture

Molecular Characterization and Enological Potential of A High Lactic Acid-Producing Lachancea thermotolerans Vineyard Strain

Lactic acid production is an important feature of the yeast Lachancea thermotolerans that has gained increasing interest in winemaking. In particular, in light of climate change, the biological acidification and ethanol reduction by the use of selected yeast strains may counteract the effect of global warming in wines. Here, the enological potential of a high lactate-producing L. thermotolerans strain (P-HO1) in mixed fermentations with S. cerevisiae was examined. Among the different inoculation schemes evaluated, the most successful implantation of L. thermotolerans was accomplished by sequential inoculation of S. cerevisiae, i.e., at 1% vol. ethanol. P-HO1produced the highest levels of lactic acid ever recorded in mixed fermentations (10.4 g/L), increasing thereby the acidity and reducing ethanol by 1.6% vol. L. thermotolerans was also associated with increases in ethyl isobutyrate (strawberry aroma), free SO2, organoleptically perceived citric nuances and aftertaste. To start uncovering the molecular mechanisms of lactate biosynthesis in L. thermotolerans, the relative expressions of the three lactate dehydrogenase (LDH) paralogous genes, which encode the key enzyme for lactate biosynthesis, along with the alcohol dehydrogenase paralogs (ADHs) were determined. Present results point to the possible implication of LDH2, but not of other LDH or ADH genes, in the high production of lactic acid in certain strains at the expense of ethanol. Taken together, the important enological features of P-HO1 highlighted here, and potentially of other L. thermotolerans strains, indicate its great importance in modern winemaking, particularly in the light of the upcoming climate change and its consequences in the grape/wine system