EFFECT OF CONCENTRATION ON THE RHEOLOGY AND SERUM SEPARATION OF TOMATO SUSPENSIONS

Microstructure and bioaccessibility of different carotenoid species as affected by high pressure homogenisation: a case study on differently coloured tomatoes

The effect of high pressure homogenisation (HPH) on structure (Bostwick consistency, particle size distribution and microstructure) and carotenoid in vitro bioaccessibility of different tomato pulps was investigated. HPH decreased tomato particle size due to matrix disruption and increased product consistency, probably due to the formation of a fibre network. Homogenisation also resulted in a decrease of in vitro bioaccessibility of lycopene, ζ-carotene, and lutein. Such decrease was attributed to the structuring effect of HPH. An inverse relation between tomato consistency and carotenoid in vitro bioaccessibility was found. This dependency was affected by carotenoid species and its localisation within the matrix. It could be observed that one matrix (e.g. (homogenised) red tomato pulp) can contain carotenoids with a very low bioaccessibility (lycopene) as well as carotenoids with a very high bioaccessibility (lutein), indicating that carotenoid bioaccessibility is not solely dependent on the matrix.

Effect of mechanical and thermal treatments on the microstructure and rheological properties of carrot, broccoli and tomato dispersions

BACKGROUND

The food industry has shown an increased interest in the manufacture of healthier and more natural food products. By tailored processing fruit and vegetables can be used as structurants thus reducing artificial gums and stabilisers. The effect of different thermal and mechanical treatments, including high-pressure homogenisation, on the microstructural and rheological properties of carrot, broccoli and tomato dispersions was studied. As part of the rheological characterisation small oscillatory deformation as well as shear flow measurements were performed.

RESULTS

Carrot and broccoli showed a different behaviour from tomato under the conditions studied. Changing the order of thermal and mechanical treatment led to microstructures with different flow properties. The resulting microstructures differed in the manner of cell wall separation: either breaking across the cell walls or through the middle lamella. High-pressure homogenisation decreased the viscosity of carrot and broccoli dispersions, while it increased the viscosity of tomato. Cryo-scanning electron microscopy showed that the cell walls of carrot and broccoli remained as compact structures after homogenisation whereas tomato cell walls were considerably swollen.

CONCLUSIONS

Based on the type of vegetable, the different processes applied led to microstructures with different rheological properties. This study shows that particle size distribution, morphology and phase volume are important parameters to explain the complex relationship between rheology and microstructure for these types of systems.

Effect of autochthonous lactic acid bacteria starters on health-promoting and sensory properties of tomato juices

Strains of Lactobacillus plantarum, Weissella cibaria/confusa, Lactobacillus brevis, Pediococcus pentosaceous, Lactobacillus sp. and Enterococcus faecium/faecalis were identified from raw tomatoes by Biolog System, partial 16S rRNA gene sequence and subjected to typing by Random Amplified Polymorphic DNA-Polymerase Chain Reaction (RAPD-PCR) analysis. Ten autochthonous strains were singly used to ferment tomato juice (TJ) via a protocol which included fermentation at 25 degrees C for 17 h and further storage at 4 degrees C for 40 days. Unstarted TJ and TJ fermented with an allochthonous strain of L. plantarum were used as the controls. All autochthonous strains grew well in TJ reaching cell densities ca. 10,000 and 10 times higher than unstarted TJ and TJ fermented with the allochthonous strain. Viscosity of TJs fermented with autochthonous strains was generally the highest, especially when started with W. cibaria/confusa which synthesized exo-polysaccharides. Overall, unstarted TJ and TJ fermented with the allochthonous strain showed marked decreases of ascorbic acid (ASC), glutathione (GSH) and total antioxidant activity (TTA) during storage. On the contrary, several TJs fermented with autochthonous strains, especially with L. plantarum POM1 and POM 35, maintained elevated values of ASC, GSH and TAA. The variation of color indexes mirrored the above behavior. TJs fermented with the above two autochthonous strains were compared to controls based on volatile components through Purge and Trap or Solid Phase Microextraction Gas Chromatography-Mass Spectrometry (PT or SPME-GC/MS) analysis. As shown by Principal Component Analysis a large number of volatiles belonging to various chemical classes markedly differentiated TJs fermented with autochthonous strains with respect to controls.

Changes in pectins and product consistency during the concentration of tomato juice to paste

Concentrating tomato juice to paste during the tomato season allows for preservation and long-term storage, but subsequent dilution for formulation of value-added products is known to result in a loss of consistency. To understand the reasons for this, samples of unconcentrated juice, processing intermediates, and concentrated paste were collected from an industrial processing plant during normal commercial production. All samples were diluted with water to 5 degrees Brix and then analyzed for consistency and pectin content. Whole juice consistency, measured with a Bostwick consistometer, decreased through the course of juice concentration, with the largest change occurring early in the process, as the juice was concentrated from 5 to 10 degrees Brix. This decrease in consistency occurred during the production of paste from both hot- and cold-break juices. The change in Bostwick value was correlated with a decrease in the precipitate weight ratio. The loss of consistency during commercial processing was not the direct result of water removal because a sample of this same 5 degrees Brix juice could be concentrated 2-fold in a vacuum oven and then diluted back to 5 degrees Brix with no change in consistency or precipitate ratio. Total pectin content did not change as the juice was concentrated to paste, but the proportion of the total pectin that was water soluble increased. The greatest increases in pectin solubility occurred during the hot break and late in the process where the evaporator temperature was the highest.