Feeding preference by the male blowfly Phormia regina for some natural foods and its relation to carbohydrate, amino acid, and alcohol content

The male blowfly, Phormia regina Meigen shows preference among a variety of natural and artificial foods. In a laboratory study preference was observed among sweet and fermenting juices as well as between liver and fish. The preferences between fresh and fermenting juices were based not only on component sugars, but also on other components, namely, amino acids, alcohol salts and presumably other chemical compounds. The preference between decaying liver and fish was probably based partly on the composition and concentration of amino acids in these foods. A variety of amino acids were found in foods and some of these amino acids were shown to be excitatory, some inhibitory and others neutral. Salts were also observed to be present in the juices; and in a laboratory study NaCl at lower concentrations acted synergestically with 0.1 M sucrose and at higher concentrations repulsive. It is suggested that feeding preference is based on several chemicals which behave either in an excitatory, additive, neutral, inhibitory or synergistic manner. The ratio of excitants to inhibitants is important in deciding the direction of preference.

---

Résumé P. regina Meigen mâle préfere certains aliments naturels ou artificiels. Au laboratoire ses préférences parmi les jus sucrés sont les suivantes: orange > miel > pomme > sucrose 0.1 M; et parmi les aliments en décomposition: sucrose 0.1 M > foie > poisson. Les jus frais sont préférés aux jus fermentés. Les préférences ne dépendent pas seulement de la nature des sucres, mais aussi des acides aminés, de l'alcool, des sels et probablement d'autres substances chimiques. Le foie contient à la fois le plus grand nombre et la concentration la plus élevée en acides aminés, ce qui explique partiellement le goût pour le foie. Expérimentalement on peut classer les acides aminés en stimulants, inhibiteurs et neutres. Des sels ont été notés dans les jus, mais aucune analyse qualitative et quantitative n'en a été faite. Mélangé à du sucrose à 0.1 M, NaCl agit en synergie aux faibles concentrations, devient neutre à 0.175 M et à des concentrations supérieures le sucrose seul est préféré au mélange avec NaCl. Cependant, un mélange de NaCl à 0.25 M (bien qu'une telle concentration soit peu probable dans des jus végétaux) avec du sucrose à 0.1 M était préféré à l'eau. Il en est déduit que les préférences alimentaires. dans la nature sont orientées par plusieurs substances chimiques qui se comportent d'une façon stimulante, additive, neutre, inhibitrice ou synergique, et que les préférences alimentaires sont relatives. Le rapport de stimulants sur inhibiteurs est important dans la détermination du sens de la préférence.

     

Effects of the high pressure of homogenization on some spoiling micro-organisms, representative of fruit juice microflora, inoculated in saline solution

Aims:  This study was aimed to investigate the effects of a high-pressure homogenization (HPH) treatment on some micro-organisms, involved in the spoilage of fruit juices.
Methods and Results:  Lactobacillus plantarum , Lactobacillus brevis , Bacillus coagulans cells, Saccharomyces bayanus , Pichia membranaefaciens and Rhodotorula bacarum were separately inoculated in a saline solution (0·9% NaCl); the initial inoculum was ca. 5 log CFU ml⁻¹. Then, the samples were processed through a homogenizer at 10–150 MPa for 1, 2 or 3 times. Yeasts were completely inactivated at 50–110 MPa with a single pass treatment, while lactic acid bacteria counts were reduced to approximately 1 log CFU ml⁻¹ after a three-steps HPH processing.
Conclusions:  Yeasts were the most sensitive micro-organisms, followed by B. coagulans . On the other hand, lactic acid bacteria appeared resistant to HPH.
Significance and Impact of the Study:  The results of this study provided some useful information on the susceptibility of microflora of juices to homogenization; moreover, they suggested that HPH could be used successfully to inactivate yeasts.     

Inactivation of Escherichia coli and Shigella in acidic fruit and vegetable juices by peroxidase systems

AIMS: To study the bactericidal properties of the lactoperoxidase (LPER)-thiocyanate and soybean peroxidase (SBP)-thiocyanate systems at low pH, their efficiency for inactivation of Escherichia coli and Shigella in acidic fruit and vegetable juices, their effect on colour stability of the juices and interaction with ascorbic acid. METHODS AND RESULTS: Three-strain cocktails of E. coli and Shigella spp. in selected juices were supplemented with the LPER or SBP system. Within 24 h at 20 degrees C, the LPER system inactivated both cocktails by > or = 5 log10 units in apple, 2-5 log10 units in orange and < or = 1 log10 unit in tomato juices. In the presence of SBP, browning was significant in apple juice and white grape juice, slight in pink grape juice and absent in orange or tomato juice. Ascorbic acid protected E. coli and Shigella against inactivation by the LPER system, and peroxidase systems significantly reduced the ascorbic acid content of juices. CONCLUSIONS: Our results suggest a different specificity of LPER and SBP for SCN-, phenolic substrates of browning and ascorbic acid in acidic juices. The LPER system appeared a more appropriate candidate than the SBP system for biopreservation of juices. SIGNIFICANCE AND IMPACT OF THE STUDY: This work may open perspectives towards the development of LPER or other peroxidases as biopreservatives in acidic foods.     

Antioxidant Properties of Fruits and Vegetables Shots and Juices: An Electron Paramagnetic Resonance Study

The antioxidant activity of some commercially available fruit and vegetable juices was evaluated with regard to their radical scavenging activity against the stable free radical 4-hydroxy-2,2,6,6-tetramethyl-l-piperidinyloxy (TEMPOL) monitored by electron paramagnetic resonance (EPR) spectroscopy. TEMPOL is a stable nitroxide free radical characterized by a well-defined EPR spectrum consisting of three peaks. The integral intensity of the EPR spectra of TEMPOL was decreased upon juice addition, and the decrease was dose dependent. EPR spectroscopy using stable free radicals provides a simple, rapid, and sensitive method for the determination of antioxidant activity of fruit and vegetable juices. The method was standardized by using the standard antioxidant compound Trolox, and the antioxidant activity of the juices was expressed as Trolox equivalents. When concentrated juices of fruits and vegetables (shots) were considered, the evaluated antioxidant activity was almost twofold higher than that of the conventional, non-concentrated ones. Fruits and vegetables shots also showed very good stability during storage. This finding indicates that natural antioxidant compounds contained in commercially available concentrated juices are not eliminated or inactivated when the juices are kept refrigerated according to the instructions of the manufacturer.     

Effect of skim milk-alginate beads on survival rate of bifidobacteria

In this study, an attempt was made to increase the survival rate of bifidobacteria entrapped in alginate in the gastrointestinal tract, and to investigate the potential industrial applications, for example lyophilized capsules and yogurt. First, the protective effect of various food additives on bifidobacterial survivability was determined after exposure to simulated gastric juices and bile salts. The additives used in this study were skim milk (SM), poly dextrose (PD), soy fiber (SF), yeast extract (YE), chitosan (CS), κ-carageenan (κ-C) and whey, which were added at 0.6% concentration (w/v) to 3% alginate-bifidobacterial solution. In the simulated gastric juices and bile salts, the protective effect of 0.6% skim milk-3% alginate (SM-A) beads on the survival rate of bifidobacteria proved to be higher than the other additives. Second, the hydrogen ion permeation was detected through SM-A vessel without bifidobacterial cells at different SM concentrations (0.2%, 0.4%, 0.6%, 0.8%, and 1.0%). There were no differences in terms of the pH decrease in SM-A vessels at 0.6%, 0.8%, and 1.0% (w/v) SM concentrations. The survival rate of bifidobacteria in SM-A beads would appear to be related to the SM buffering capacity against hydrogen ions and its tendency to reduce the pore size of bead. In this experiment, the survival rate of bifidobacteria entrapped in beads containing 0.6% SM showed the highest viability after exposure to simulated gastric juices for 3 h, thereby indicating that 0.6% SM is the optimum concentration for 3% alginate bead preparation. Third, the effect of SM-A beads on the freeze-drying and yogurt storage for 10 days was investigated. SM-A beads were found to be more efficient for freeze drying and yogurt storage than untrapped cells and the alginate bead. Consequently, the survival rate of bifidobacteria entrapped in SM-A beads was increased in simulated gastric juices, bile salts and probiotic products such as lyophilized capsules and yogurt, SM-A beads can be expected to produce high value probiotic products.     

Evaluation of differences in the aroma composition of free-run and pressed neutral grape juices obtained from Emir (Vitis vinifera L.)

In this study, the differences in the aroma compounds released after the free-run and pressed juices of cv. Emir grape (Vitis vinifera L.) were evaluated. Aroma compounds were obtained by liquid-liquid extraction with CH(2) Cl(2) , and then analyzed by gas chromatography (GC) and gas chromatography/mass spectrometry (GC/MS). According to the results, pressing uniformly increased the levels of the aromatic constituents, but this treatment lowered the grape juice quality for winemaking by increasing the total phenolic compounds, browning index, and C(6) -alcohol levels (green-herbaceaous odor) as compared to the free-run juice. From all the aroma compounds identified in both juices, hexan-1-ol, (E)-hex-2-en-1-ol, isobutanol, isoamyl alcohol, and 2-phenylethanol were the most abundant volatile compounds.     

Bacteriocins from lactic acid bacteria and their potential in the preservation of fruit products

Bacteriocins produced by lactic acid bacteria (LAB) are well-recognized for their potential as natural food preservatives. These antimicrobial peptides usually do not change the sensorial properties of food products and can be used in combination with traditional preservation methods to ensure microbial stability. In recent years, fruit products are increasingly being associated with food-borne pathogens and spoilage microorganisms, and bacteriocins are important candidates to preserve these products. Bacteriocins have been extensively studied to preserve foods of animal origin. However, little information is available for their use in vegetable products, especially in minimally processed ready-to-eat fruits. Although, many bacteriocins possess useful characteristics that can be used to preserve fruit products, to date, only nisin, enterocin AS-48, bovicin HC5, enterocin 416K1, pediocin and bificin C6165 have been tested for their activity against spoilage and pathogenic microorganisms in these products. Among these, only nisin and pediocin are approved to be commercially used as food additives, and their use in fruit products is still limited to certain countries. Considering the increasing demand for fresh-tasting fruit products and concern for public safety, the study of other bacteriocins with biochemical characteristics that make them candidates for the preservation of these products are of great interest. Efforts for their approval as food additives are also important. In this review, we discuss why the study of bacteriocins as an alternative method to preserve fruit products is important; we detail the biotechnological approaches for the use of bacteriocins in fruit products; and describe some bacteriocins that have been tested and have potential to be tested for the preservation of fruit products.     

Occurrence of microorganisms of public health and spoilage significance in fruit juices sold in retail markets in Greece

Fruit juices are an important part of the modern diet in many countries. However, few data are available concerning the microbiological quality of the fruit juices sold in Greece. Using standard microbiological procedures, we conducted a bacteriological survey of commercially sold, pasteurized, shelf-stable fruit juices from retail markets. A total of 120 samples of fruit juices sold in various retail markets were examined for their bacteriological quality. The pH of the tested juices was 2.4–4.8. Bacteria were isolated from 51 samples (42.5%) and fungi from 78 samples (65%). Escherichia coli O157:H7 was detected in four of the analyzed samples (3.34%), and Staphylococcus aureus was detected in four different samples (3.34%). In 11 samples (9.1%), the total number of microorganisms detected was as high as 125 colony-forming units (CFU). Acidophilic microorganisms were isolated from 26 samples (21.7%) and Blastomyces was detected in 46 samples (38.3%). All samples were negative for Lactobacillus, Clostridium perfrigens, Salmonella spp., Bacillus cereus, total coliforms, E. coli, and Listeria monocytogenes.Many of the microorganisms detected may cause disease in humans; thus, a number of the tested samples did not meet the Greek guidelines for the microbiological quality of juices. Use of a Hazard Analysis Critical Control Point (HACCP) system should be generally introduced into the juice industry sector to improve the quality of fruit juices, as well as other manufactured foods.     

Analysis of wines, grape juices and cranberry juices forAlternaria toxins

Sixty six samples of red and white wine from Ontario (VQA), British Columbia (VQA), Québec (“vins artisanaux”), imported wines (from Italy, South America and USA) and Canadian and US grape and cranberry juices were analysed for theAlternaria mycotoxins alternariol (AOH) and alternariol monomethyl ether (AME). After cleanup on aminopropyl SPE columns, AOH and AME were initially determined by reversed phase LC with UV detection. Positive sample extracts were re-analysed by LC-tandem negative ion electrospray mass spectrometry (MS/MS) in multiple reaction mode. Overall mean method recoveries measured by LC-UV were 93% for AOH and 81% for AME. Limits of detection in wine (and juice) by LC-UV for AOH were 0.8 (0.4) ng/ml and for AME were 0.5 (0.4) ng/ml; they were below 0.01 ng/ml by LC-MS/MS. As determined by LC-MS/MS, AOH was found in 13/17 Canadian red wines at levels of 0.03 to 5.02 ng/ml and in 7/7 imported red wines at 0.27–19.4 ng/ml, usually accompanied by lower concentrations of AME. Red grape juices (5 positive/10 samples) contained only sub ng/ml levels of AOH or AME except for one sample (39 ng AME/ml). White wines (3/23 samples), white grape juices (0/4 samples) and cranberry juices (1/5 samples) contained little AOH/AME (≤1.5 ng/ml). Presented at the World Mycotoxin Forum, Noordwijk, The Netherlands, November 10–11, 2005     

Direct enzymatic glucosylation of naringin in grapefruit juice by alpha-D-glucosidase from the marine mollusc Aplysia fasciata

The enzymatic glucosylations of naringin, performed using alpha-D-glucosidase, identified in the Mediterranean mollusc Aplysia fasciata is reported. The enzyme actively operates on maltose and has an interesting transglycosylation potential using this donor. We also investigated the use of this marine alpha-glucosidase for a food-compatible glucosylation of naringin to produce new enzymatically modified carbohydrate possessing naringin derivatives. The regioselective formations of the beta-gluco-C6 alpha-glucosyl derivative and of the corresponding isomaltosyl diglucoside of naringin were obtained in high yield and efficiency of reaction. Suspensions of naringin can be used up to approximately 90 mg/mL initial acceptor concentration. In different experiments it was demonstrated that the enzyme was still active after 48 h in presence of this high amount of acceptor and that one of the diasteromers of the naringin is preferred by the enzyme from A. fasciata during glucosylation/deglucosylation enzymatic steps. Finally, the feasibility of efficient naringin glucosylation in grapefruit juice was also demonstrated at optimal pH of the enzyme and low maltose concentrations.