Von Bezold assimilation effect reverses in stereoscopic conditions

Lightness contrast and lightness assimilation are opposite phenomena: in contrast, grey targets appear darker when bordering bright surfaces (inducers) rather than dark ones; in assimilation, the opposite occurs. The question is: which visual process favours the occurrence of one phenomenon over the other? Researchers provided three answers to this question. The first asserts that both phenomena are caused by peripheral processes; the second attributes their occurrence to central processes; and the third claims that contrast involves central processes, whilst assimilation involves peripheral ones. To test these hypotheses, an experiment on an IT system equipped with goggles for stereo vision was run. Observers were asked to evaluate the lightness of a grey target, and two variables were systematically manipulated: (i) the apparent distance of the inducers; and (ii) brightness of the inducers. The retinal stimulation was kept constant throughout, so that the peripheral processes remained the same. The results show that the lightness of the target depends on both variables. As the retinal stimulation was kept constant, we conclude that central mechanisms are involved in both lightness contrast and lightness assimilation

Zymomonas mobilis in Bread Dough: Characterization of Dough Leavening Performance in Presence of Sucrose

Zymomonas mobilis, because of its fermentative metabolism, has potential food applications in the development of leavened baked goods consumable by people with adverse responses to Saccharomyces cerevisiae. Since Z. mobilis is not able to utilize maltose present in flour, the effect of sucrose addition (2.5 g/100 g flour) on bread dough leavening properties was studied. For comparison purposes, leavening performances of S. cerevisiae with and without sucrose were also investigated. Doughs leavened by Z. mobilis without sucrose addition showed the lowest height development (14.95 +/- 0.21 mm) and CO2 production (855 +/- 136 mL). When sucrose was added, fermentative performances of Z. mobilis significantly (p < 0.05) improved (+80% and +85% of gas production and retention, respectively), with a dough maximum height 2.6 times higher, results indicating that Z. mobilis with sucrose can be leavened in shorter time with respect to the sample without addition. S. cerevisiae did not benefit the sucrose addition in terms of CO2 production and retention, even if lag leavening time was significantly (p < 0.05) shorter (about the half) and time of porosity appearance significantly (p < 0.05) longer (about 26%) with respect to S. cerevisiae alone. Results demonstrate that in the presence of sucrose, Z. mobilis can efficiently leaven a bread dough, thus providing innovation possibilities in the area of yeast-free leavened products

Can Zymomonas mobilis Substitute Saccharomyces cerevisiae in Cereal Dough Leavening?

Baker\u2019s yeast intolerance is rising among Western populations, where Saccharomyces cerevisiae is spread in fermented food and food components. Zymomonas mobilis is a bacterium commonly used in tropical areas to produce alcoholic beverages, and it has only rarely been considered for dough leavening probably because it only ferments glucose, fructose and sucrose, which are scarcely present in flour. However, through alcoholic fermentation, similarly to S. cerevisiae, it provides an equimolar mixture of ethanol and CO\u2082 that can rise a dough. Here, we propose Z. mobilis as a new leavening agent, as an alternative to S. cerevisiae, overcoming its technological limit with different strategies: (1) adding glucose to the dough formulation; and (2) exploiting the maltose hydrolytic activity of Lactobacillus sanfranciscensis associated with Z. mobilis. CO\u2082 production, dough volume increase, pH value, microbial counts, sugars consumption and ethanol production were monitored. Results suggest that glucose addition to the dough lets Z. mobilis efficiently leaven a dough, while glucose released by L. sanfranciscensis is not so well fermented by Z. mobilis, probably due to the strong acidification. Nevertheless, the use of Z. mobilis as a leavening agent could contribute to increasing the variety of baked goods alternative to those leavened by S. cerevisiae

Cellulose nano-fibers (CNF) - Sakacin-A active material: production, characterization and application in storage trials of smoked salmon

BACKGROUND: Sakacin-A due to its specific antimicrobial activity may represent a good candidate to develop active packagingsolutions for food items supportingListeriagrowth. In the present study a protein extract containing the bacteriocin sakacin-A,produced byLactobacillus sakeiLb 706 in a low-cost culture medium containing deproteinized cheese whey, was adsorbed ontocellulose nanofibers (CNFs) to obtain an active material to be used as a mat (or a separator) in direct contact with foods.RESULTS: The applied fermentation conditions allowed 4.51g L 121of freeze-dried protein extract to be obtained, characterizedby an antimicrobial activity of near 16 700 AU g 121, that was used for the preparation of the active material by casting. The activematerial was then characterized by infrared spectra and thermogravimetric analyses. Antimicrobial trials were carried outinvitrousingListeriainnocuaasindicatorstrain;resultswerealsoconfirmedinvivo,employingsmokedsalmonfilletsintentionallyinoculated withListeria innocua: its final population was reduced to about 2.5 \u2013 3 Log cycles after 28 days of storage at 6 18Cinpresence of sakacin-A, compared with negative control mats produced without the bacteriocin extract.CONCLUSION: This study demonstrates the possibility of producing an antimicrobial active material containing sakacin-Aabsorbed onto CNFs to decreaseListeriapopulation in smoked salmon, a ready-to eat-food product

From Cheese Whey Permeate To An Anti-Listeria Food Packaging Device: Bacterial Cellulose Nanocrystals/Sakacin-A Conjugates (Nanosak)

In the present project cheese whey permeate (CWP), the residual by-product obtained by extraction of whey proteins from cheese whey, was used as substrate for the growth of bacterial species that produce two appealing molecules: the anti-listerial bacteriocin sakacin-A and bacterial cellulose (BC). BC is then turned into nanocrystals (BCNCs) that are finally conjugated with sakacin-A to obtain an innovative antimicrobial device for food which could support Listeria monocytogenes growth. Sakacin-A was produced by Lactobacillus sakei DSMZ 6333 in liquid cultures. The highest bacteriocin production (around 300 AU/mL) was achieved after 9 h at 26\ub0C; a food-grade, salt-free enriched sakacin-A extract was obtained by using a gravity reverse phase chromatography. BC was produced by Komagataeibacter xylinus DSMZ 2325 by static fermentation of CWP in presence of 0.5 U/mL of \u3b2-galactosidase at 30\ub0C; after 7 days, BC yield was around 7 g/L. BCNCs were then obtained by acid hydrolysis mediated by sulfuric acid, with the goal of removing the amorphous regions of BC and introduce a net negative charge by esterification on the hydroxyl group on C6. BCNCs/sakacin-A conjugates were prepared by exploiting their opposite charge: enriched sakacin-A extract was mixed with BCNCs and, after incubation, conjugates collected by centrifugation have a specific activity of 100 AU/mg BCNCs. Among all peptides present in the enriched sample, sakacin-A appears to preferentially absorb onto BCNCs, thus allowing its further purification. Sakacin-A as well its BCNCs conjugates were then included in a hydroxypropil-cellulose coating spread onto paper sheets at a concentration of 5 and 25 AU/cm2. The addition of the coating did not bring any significant change in the oxygen barrier properties of the cellulosic substrate. In a similar way, the static contact angle of both uncoated and coated substrate was of approximately 130\ub0. However, the presence of BCNCs seemed to increase the swelling phenomenon of the coating. Sakacin A was also included in whey, caseine and cellulose derived matrices to prepare films and coatings with diverse results. The kinetics of Sakacin-A released from active films to aqueous food was analyzed by immersion of samples in water (as simulant) and measuring the anti-Listeria activity of the simulant after increasing times of exposure. In vitro and in vivo antimicrobial trials were carried out on real food products demonstrated their anti-listerial effectiveness, proving that the developed devices can contribute to increase shelf life, quality and safety of perishable foods

I principali indirizzi della psicologia contemporanea

Appunti raccolti da Fabio Metell