Removal of soy protein-bound phospholipids by a combination of sonication, β-cyclodextrin,and phospholipase A2 treatments

One of the contributing factors to generation of off-flavours in soy protein isolate (SPI) during storage is autoxidation of residual amounts of phospholipids present in SPI. Thus, removal of phospholipids from SPI is a likely first step to improve its flavour stability and enhanced utilisation of SPI in food products. We describe a β-cyclodextrin-based (βCD) process to remove protein-bound phospholipids and free fatty acids in SPI. Treating SPI solution (8%) with 10 mM βCD alone at pH 8.0 decreased the phospholipid content of SPI by about 36%. A greater than 99% removal of phospholipids and free fatty acids was achieved by using a combination of treatments involving sonication of the SPI solution for 5 min at 50 °C followed by treatment with phospholipase A₂ and βCD. SPI prepared by this method was white in colour. The results presented here offer a process for removing residual off-flavour causing phospholipids from soy protein.     

Establishment of a real-time PCR method for quantification of geosmin-producing Streptomyces spp. in recirculating aquaculture systems

Geosmin and 2-methylisoborneol (MIB) have been associated with off-flavour problems in fish and seafood products, generating a strong negative impact for aquaculture industries. Although most of the producers of geosmin and MIB have been identified as Streptomyces species or cyanobacteria, Streptomyces spp. are thought to be responsible for the synthesis of these compounds in indoor recirculating aquaculture systems (RAS). The detection of genes involved in the synthesis of geosmin and MIB can be a relevant indicator of the beginning of off-flavour events in RAS. Here, we report a real-time polymerase chain reaction (qPCR) protocol targeting geoA sequences that encode a germacradienol synthase involved in geosmin synthesis. New geoA-related sequences were retrieved from eleven geosmin-producing Actinomycete strains, among them two Streptomyces strains isolated from two RAS. Combined with geoA-related sequences available in gene databases, we designed primers and standards suitable for qPCR assays targeting mainly Streptomyces geoA. Using our qPCR protocol, we succeeded in measuring the level of geoA copies in sand filter and biofilters in two RAS. This study is the first to apply qPCR assays to detect and quantify the geosmin synthesis gene (geoA) in RAS. Quantification of geoA in RAS could permit the monitoring of the level of geosmin producers prior to the occurrence of geosmin production. This information will be most valuable for fish producers to manage further development of off-flavour events.     

Development of a solid phase microextraction protocol for the GC–MS determination of volatile off-flavour compounds from citral degradation in oil-in-water emulsions

The conditions for headspace solid phase microextraction (HS-SPME) analysis of volatile off-flavour compounds in citral emulsion were determined. Type of SPME phase (65 μm PDMS/DVB, 100 μm PDMS and 75 μm CAR/PDMS), adsorption temperature and salt concentration were significant factors affecting total peak area in the gas chromatogram and optimised in one factor experiments. Then, adsorption temperature (30–50 °C), adsorption time (20–40 min), and salt concentration (0–6 M) were studied to develop HS-SPME condition for obtaining the highest extraction efficiency. PDMS/DVB in 65 μm was the optimum fiber because of high adsorption efficiency and good reproducibility. The optimal condition was adsorption at 50 °C for 40 min and 6 M salt added to sample. Good Linearity, high recovery, good reproducibility and low limit of detection (LOD) for all off-odour compounds according to the optimised SPME conditions indicated that the SPME procedure was applicable for the analysis of the degraded citral products in headspace volatile of emulsion.     

Effects of α-tocopherol level in raw venison on lipid oxidation and volatiles during storage

Relationships between α-tocopherol concentration in the muscle and development of lipid oxidation or volatiles in raw venison were studied. Fourteen Japanese Shika Deer (Cervus nippon) were fed various amounts (0–3.0 g of α-tocopheryl acetate per animal) during the different periods (0–37 days) and then M. longissimus thoracium et lumborum (LD muscles) with a range of α-tocopherol concentrations (4.1–15.1 mg/kg tissue) were obtained. For stabilizing the lipid during storage for 11 days under air, over ca. 9 mg of α-tocopherol per kg tissue were required based on levels of 2-thiobarbituric acid reacting substances (TBARS) numbers. Nine compounds were identified in headspace volatiles, and one of the volatiles was hexanal which has been recognized as off-flavour component. For depressing the hexanal evolution, at least ca. 9 mg of α-tocopherol per kg tissue were also required for 11 days’ storage. This value was much higher than other species. The reasons for higher requirement of α-tocopherol were possibly due to the higher concentration of unsaturated fatty acid and myoglobin in venison.     

Production of indole by wine-associated microorganisms under oenological conditions

A high concentration of indole has been linked to ‘plastic-like’ off-flavour in wines, predominantly in wines produced under sluggish fermentation conditions. The purpose of this study was to determine the ability of yeast and bacteria to form indole and whether tryptophan was required for indole accumulation during winemaking. Wine-associated yeast and bacteria species (Saccharomyces cerevisiae, Saccharomyces bayanus, Candida stellata, Hanseniaspora uvarum, Kluyveromyces thermoloterans, Oenococcus oeni, Lactobacillus lindneri, Pediococcus cerevisiae and Pediococcus parvulus) were screened for their potential to generate indole during alcoholic or malolactic fermentation. Tryptophan was required for the accumulation of indole in chemically defined medium, and all yeast and bacteria fermentations were able to accumulate indole. C. stellata showed the greatest potential for indole formation (1033 μg/L) and among the bacteria, the highest concentration was generated by L. lindneri (370 μg/L). Whether primary fermentation is the principle cause of indole formation remains to be determined. We hypothesise that during an efficient fermentation, indole is removed through catabolic metabolism, but, when a sluggish fermentation arises, non-Saccharomyces species might produce excess indole that is still present by end of fermentation.     

Evidence of 4-ethylcatechol as one of the main phenolic off-flavour markers in French ciders

A new HPLC method using a diode array detector was developed and validated to quantify 4-ethylphenol, 4-vinylphenol, 4-ethylguaiacol, 4-vinylguaiacol and 4-ethylcatechol in cider. The procedure was linear up to 150 mg/l for each of the five volatile phenols, precise (RSD < 2.9%) and sensitive, with limits of detection between 0.03 and 0.10 mg/l; moreover, it did not require any sample preparation. This method was applied to 11 phenolic off-flavour defective ciders. In these ciders, the main volatile phenol corresponded to 4-ethylcatechol. Moreover, the observed concentrations (maximum of 164 mg/l) indicated, for the first time, that this compound is an important phenolic off -flavour marker in cider. Then, volatile phenols concentrations were determined for 47 French commercial ciders and showed mean quantities of 3.2 (4-EC), 0.8 (4-EP), 0.1 (4-EG), 0.2 (4-VP) and 0.3 mg/l (4-VG). The majority of the tested commercial ciders presented low volatile phenol levels.     

4-Ethylphenol and 4-ethylguaiacol depletion in wine using esterified cellulose

The ability of cellulose acetate, cellulose acetate propionate (CAP), cellulose acetate butyrate and cellulose propionate (CP) fibres to reduce 4-ethylphenol and 4-ethylguaiacol, causing the off-flavour named “Brett character”, was studied. CAP and CP performed best in a preliminary comparative test. The former was chosen because of its more favourable FDA classification for food contact substances. CAP effectiveness was studied in relation to the reduction in volatile phenols with doses of up to 20 g/l and wine contact times of up to 60 min. Using 4 g/l, reduction of both phenols was, on average, 31–32% in defective red wines. Wine treatment affected neither colour nor total proanthocyanidins and catechins, and wines were judged to be better than the corresponding spoiled controls. CAP fibre can be regenerated by washing with ethanol or aqueous solution (pH 12), without notable changes in depletion efficiency. The technological characteristics of CAP and, to a lesser extent, CP offer interesting prospects for producing filtration beds, pads and membranes for the treatment of wines and beverages affected by “Brett character”.