DETERMINATION OF PRACTICALLY SIGNIFICANT DIFFERENCES IN THE SENSORILY PERCEIVED CONSISTENCY OF SEMILIQUID FOODS1

The consistency of commercial salad dressing, chocolate pudding and mustard samples before and after controlled disruption was assessed by squeezing flow viscometry and evaluated sensorily by an untrained panel. The instrumental parameters were the apparent stress at 1.5 and 1.0 mm height and the apparent residual stress after 60 and 120 s relaxation (at 1.0 mm height). The panelists were asked to identify the sample(s) with the stronger consistency in a triangular test. The percent correct identifications was plotted against the difference in the magnitude of the instrumental parameters and their ratios. The scatter of these plots suggests that the effective stimulus for consistency perception was primarily the overall resistance to deformation or flow and to a much lesser extent to more subtle rheological characteristics like the ‘degree of solidity'. In the range of consistencies examined, the detection thresholds were on the order of 0.5‐0.7 kPa and 0.4‐0.6 kPa at 1.0 and 1.5 mm height, respectively. They corresponded to stress ratios on the order of 0.75‐0.85. Results of this kind will enable setting objective standards for the consistency of commercial semi liquid foods and tolerance margins to deviations from them.     

VARIETAL AROMA COMPOUNDS OF VITIS VINIFERA CV. KHAMRI GROWN IN TUNISIA

ABSTRACT

The aroma composition of the grape juice of Khamri, a native variety of Vitis vinifera grown in Tunisia, was investigated for the first time. A total of 27 free and 20 glycosidically bound compounds were identified by gas chromatography‐mass spectrometry. According to the obtained results, the aroma compounds were C6 alcohols, benzene compounds, terpenes, acids and norisoprenoids. On the basis of gas chromatography‐olfactometry, these compounds were grouped, according to volatiles exhibiting the identical odor quality, into 10 groups of the same character (aromatic series) as a way of establishing an aroma profile for the studied variety. The high glycosidically bound norisoprenoid concentrations and the absence of the bound form of the acids were a positive factor for the Khamri variety potential aroma.

PRACTICAL APPLICATIONS

This article aimed on the identification of the unknown Tunisian grapevine varieties that are very well adapted to the arid conditions and that could have a good quality. The discovery of unknown autochthonous grapevine varieties with good aroma and pomological characteristics could be of great importance for the agriculture sector all over the world especially the arid regions.

     

DIFFERENTIAL SCANNING CALORIMETRY DETECTION OF HIGH OLEIC SUNFLOWER OIL AS AN ADULTERANT IN EXTRA-VIRGIN OLIVE OIL

Differential scanning calorimetry (DSC) was employed to detect high oleic sunflower oil (HOSo) as an adulterant in extra-virgin olive oil (EVOo) by means of cooling and heating thermograms. Addition of HOSo did not significantly alter cooling profiles of EVOo except for onset temperature of crystallization, which was significantly shifted toward lower temperature at 40% of adulterant addition. At the same percentage of adulteration, the heating profile of EVOo was significantly changed as the major endotherm broadened and the minor event became smaller and less evident. Cooling thermograms of pure oils and their admixtures were deconvoluted into three constituent exothermic peaks in an attempt to detect addition of HOSo at levels lower than 40%. Thermal properties of the two lower-temperature exotherms (area percentage, offset temperature and range of transition) were significantly changed at ≥ 20% of HOSo substitution, suggesting that DSC can be employed to detect this oil as an EVOo adulterant.

PRACTICAL APPLICATIONS

Adulteration of extra-virgin olive oil (EVOo) with cheaper oils from other vegetable sources or seeds, as well as with lower quality olive oils, is a serious concern for oil suppliers and consumers and requires the use of new analytical techniques for their detection. Differential scanning calorimetry (DSC) exhibits some advantages over the classical analytical methods as it does not require sample preparation and use of solvents, thus resulting in a reduced environmental impact. Results suggested that its application to the detection of EVOo adulteration with high oleic sunflower oil, a vegetable oil largely employed for this type of fraud, is promising with the support of the deconvolution analysis of cooling thermograms.     

Characterization and Distribution of Aerobic, Spore-Forming Bacteria from Cacao Fermentations in Bahia

Aerobic spore forming bacteria isolated from traditional cacao fermentations in Bahia were identified in the genus Bacillus: B. subtilis, B. licheniformis, B. firmus, B. coagulans, B. pumilus, B. macerans, B. polymyxa, B. laterosporus, B. stearothermophilus, B. circulans, B. pasteurii, B. megaterium, B. brevis, and B. cereus. In the first 8 hr of the fermentations, similar percentages of ten species were found in the distribution. During the fermentation process the amount of spore-forming bacteria increased and B. subtilis, B. circulans, and B. licheniformis appeared more frequently.     

SENSORY THRESHOLDS OF CONSISTENCY OF SEMILIQUID FOODS: EVALUATION BY SQUEEZING FLOW VISCOMETRY*

Identification of subtle textural differences or changes in foods in isolation has been a difficult task because they are usually accompanied by differences or changes in other sensory properties. Textural modification of semi liquid foods can easily be produced by mechanical means without affecting their taste and appearance. The changes can be then quantified using squeezing flow viscometry without introducing new uncontrolled modifications. Comparison of the measurements with sensory evaluations of the same samples can establish the threshold of sensory detection, at least in principle. To test this hypothesis, the consistency of practically intact mayonnaise, tomato paste, yogurt and strawberry jam of two commercial brands each were evaluated by squeezing flow viscometry using an Instron UTM. Other samples of the same brands were stirred mildly to modify their consistency and then compared with the undisturbed samples. The textural differences were expressed in terms of the apparent stress at three compressed specimen heights, and the residual stress after 60 and 120 s at the final height. Relatively large differences, as judged by these mechanical measures were also detected by an untrained sensory panel, but the ‘correct identifications’ never reached a 100%. In the case of the two different brands of yogurt, the panel failed to establish the existence of differences, which were clearly detected by the instrument. This suggests that not every difference, detectable instrumentally, has a corresponding sensory response. Although the number of results in this preliminary work was too small to establish the exact threshold for sensory detection, the methodology seems to be appropriate for such a purpose. This is because of the high reproducibility of the squeezing flow parameters and their sensitivity to even subtle difference in the tested specimens consistency.     

Characterisation of three temperate phages released from the same Lactobacillus paracasei commercial strain

Lysogeny entails more economical and technological risks in probiotic Lactobacillus casei/paracasei bacteria than in other lactic acid bacteria, due to economic value. Lysogeny is widely spread among L. casei/paracasei strains. Siphophages C_L1 and C_L2, isolated from noninfected lysed‐cultures of commercial L. paracasei A, are thermoresistant, have identical host spectrum, latent and burst times, whereas burst sizes are 148 and 85, respectively. Mitomycin C induction of L. paracasei A yielded prophage iA2, whose presence was confirmed on the strain genome and whose restriction patterns differed from phages C_L1 and C_L2. The latter shared several restriction fragments, probably indicating a common origin.     

SUPERCRITICAL CARBON DIOXIDE SELECTIVITY TO FRACTIONATE PHENOLIC COMPOUNDS FROM THE DRY ETHANOLIC EXTRACT OF PROPOLIS

The global yield and composition of extracts obtained by supercritical carbon dioxide (SC-CO₂) extraction from a dry ethanolic extract of propolis were measured in order to determine the possibility of using SC-CO₂ to fractionate components of interest present in these extracts. The global yield extraction was measured, and also the concentrations of the following phenolic compounds in the resulting supercritical fluid extracts (SFEs): 3,5-diprenyl-4-hydroxycinnamic acid (known as artepillin C), 3-prenyl-4-hydroxycinnamic acid, 4-hydroxycinnamic acid ( p- coumaric acid) and 4-methoxy-3,5,7-trihydroxyflavone (kaempferide), of which artepillin C was the target component of greatest interest. The results showed extraction yields between 3.82 (at 150 bar) and 13.07% (at 350 bar), which could be highly correlated with the density of the SC-CO₂ at a constant temperature of 60C. The resulting concentrations in the SFE indicated that the selectivity of the carbon dioxide could be manipulated, and it was more selective at lower pressures, although with lower extraction yields.

PRACTICAL APPLICATIONS

Supercritical fluid extraction is an interesting process for the production of natural extracts because it is a clean process, and extractions using carbon dioxide (CO₂) as the solvent have been gaining attention in recent years. This study presented important aspects with respect to the fractionation of a dry ethanolic extract of propolis using supercritical carbon dioxide, and it is important to explore the potential applications of propolis extracts and the biological properties of its fractions in the food, pharmaceutical and cosmetic industries, such as in dental hygiene products, wound healing creams and antibacterial soaps.