Search results

Este texto resulta dos conhecimentos que foram sendo consolidados no decorrer do Projecto PAMAF 6006 "Optimização das operações de pós colheita par um aumento da rentabilidade na comercialização de Cerejas". Este Projecto reúne colaboradores do ISA (DAIAT e DPAA), do IST (DEM e DEQ), da ESACB (Fitotecnia), da DRAEDM e da DRATM. Os seus principais objectivos são: 1. Aumentar o tempo de vida útil da cereja: Melhorar procedimentos na colheita para minimizar os danos mecânicos e térmicos nos frutos; Utilização de frio de forma eficaz (pré arrefecimento e conservação a temperatura baixa). 2. Introdução de mais valias na comercialização de cerejas: Calibragem; Embalagem; Desenvolvimento de produtos para uso do refugo das operações de selecção e calibragem. Este texto irá incidir na discussão de alguns aspectos a considerar na marcação da data de colheita e na conservação de cereja para o mercado de frescos.

Whey protein isolate and glycerol were mixed to form a matrix to incorporate antimicrobial agents and produce edible films with antimicrobial activity against Listeria monocytogenes strains isolated from cheeses. Various organic acids were used to decrease pH down to approximately 3. In a preliminary assay without nisin, the effect of each organic acid was evaluated with respect to the rheological properties of the film solutions and the inhibitory and mechanical properties of the films. Lactic, malic, and citric acids (3%, wt/vol), which were used in a subsequent study of their combined inhibitory effect with nisin (50 IU/ml), had significantly higher antilisterial activity (P , 0.05) compared with the control (2 N HCl, 3% [wt/vol], with nisin). The largest mean zone of inhibition was 4.00 6 0.92 mm for malic acid with nisin. Under small-amplitude oscillatory stress, the proteinglycerol-acid film solutions exhibited a predominantly viscous behavior or a weak gel behavior, with the storage modulus (G9) slightly higher than the loss modulus (G0). The malic acid–based solution was the only one whose viscosity was not influenced by the addition of nisin. The addition of nisin resulted in a nonsignificant (P . 0.05) increase in the percentage of elongation at break. Results from tensile and puncture stress were variable, but in general no significant differences were found after the incorporation of nisin. The overall results support the use of malic acid with nisin to produce effective antimicrobial films to control L. monocytogenes growth.

The inhibitory effects of nisin, natamycin and malic acid, incorporated in whey protein films with pH 3, were investigated alone or with addition of sucrose esters, Tween80 or EDTA. Water vapour permeability measurements and mechanical and rheological tests were also assessed. EDTA and Tween80 did not significantly (P < 0.05) influence the inhibitory activity of films against Pseudomonas aeruginosa and Yarrowia lipolytica in contrast with the improved effect against Listeria monocytogenes, Penicillium commune and Penicillium chrysogenum. Sucrose esters reduced significantly (P < 0.05) the inhibitory effect for Y. lipolytica and Penicillium spp. The present work provides an antimicrobial film formulation with potential to be a hurdle against spoilage and pathogenic microorganisms isolated from cheese surface.

The bioactivity of natural antioxidants from plant extracts is well known. Still, the effectiveness of these natural antioxidants, namely polyphenols, depends on preserving their stability, which can be increased by microencapsulation. The aim of this study was to protect natural antioxidants from the aqueous extract of Portuguese wild herb Pterospartum tridentatum by encapsulation in alginate hydrogel microbeads. Microbeads were prepared by electrostatic extrusion technique: plain Ca-alginate microbeads and Ca-alginate microbeads with 10 and 20 mass% of inulin as a filler substance. Total polyphenol content (TPC) and the radical scavenging activity using ABTS and DPPH cations were determined. The release studies of polyphenols from microbeads were performed. The microbeads were analysed by Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM) and optical microscopy (OM). Encapsulation efficiency (EE) was in the range from 49 to 73%. Antioxidant assays and release studies showed that alginate-inulin microbeads appeared to be suitable dosage forms. The inclusion of inulin contributes to improved microbeads structure, as well as to nutritional values of food. Thereby, potential applications of these microbeads could be functional food products, an increasingly valued market.