Agnese Panozzo

Colour and carotenoid changes of pasteurised orange juice during storage.

The correlation of carotenoid changes with colour degradation of pasteurised single strength orange juice was investigated at 20, 28, 35 and 42°C for a total of 32 weeks of storage. Changes in colour were assessed using the CIELAB system and were kinetically described by a zero-order model. L(∗), a(∗), b(∗), ΔE(∗), Cab(∗) and hab were significantly changed during storage (p<0.05). Activation energies for all colour parameters were 64-73 kJ mol(-1). Several carotenoids showed important changes and appeared to have different susceptibilities to storage. A decrease of β-cryptoxanthin was observed at higher temperatures, whereas antheraxanthin started to decrease at lower temperatures. Depending on the time and temperature, changes in carotenoids could be due to isomerisation reactions, which may lead to a perceptible colour change. Although the contribution of carotenoids was recognised to some extent, other reactions seem of major importance for colour degradation of orange juice during storage.

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 ultrasound treatment, oil addition and storage time on lycopene stability and in vitro bioaccessibility of tomato pulp.

This study was performed to investigate the influence of ultrasound processing on tomato pulp containing no sunflower oil, or increasing amounts (i.e. 2.5%, 5% and 10%), on lycopene concentration and in vitro bioaccessibility at time zero and during storage at 5 °C. Results confirmed previous findings in that ultrasonication was responsible for cell breakage and subsequent lycopene release in a highly viscous matrix. Neither the ultrasound process nor oil addition affected lycopene concentration. A decrease of approximately 35% lycopene content occurred at storage times longer than 15 days, due to isomerisation and oxidation reactions. No differences in lycopene in vitro bioaccessibility were found between the untreated and ultrasonically treated samples; this parameter decreased as a consequence of oil addition. Losses of lycopene in vitro bioaccessibility ranging between 50% and 80% occurred in the untreated and ultrasonically treated tomato pulps with and without oil during storage, mainly due to carotenoid degradation.

Effect of ultraviolet processing on selected properties of egg white.

The effect of ultraviolet processing (10.6 and 63.7 kJ m(-2)) on selected properties of egg white (absorbance, particle size, protein fractions, free sulfhydryl content, immunoreactivity, viscosity, gelling and foaming properties) was investigated. Ultraviolet exposure induced the development of browning, the formation of large protein aggregates by disulfide exchange, and protein backbone cleavage. However, egg white proteins were differently sensitive to UV radiation. No changes in immunoreactivity, gelling temperature and gel firmness were observed. Independently on the UV dose, light treated egg white produced foams with higher stability. This effect was attributed to protein aggregates jamming in the fluid interstices between bubbles and/or to the higher viscosity of the aqueous phase. The latter was also associated to higher foam volume.

Lycopene and β-carotene transfer to oil and micellar phases during in vitro digestion of tomato and red carrot based-fractions

The natural structural barriers (i.e. chromoplast substructure and cell wall) in conjunction with the carotenoid hydrophobicity were investigated as factors that may play a role governing the carotenoid transfer efficiency from the tomato and red carrot matrices into the oil and micellar phases during digestion. In addition, the effect of thermal processing on the carotenoid transfer during digestion was studied. While the carotenoid transfer efficiency from the matrix into the oil phase was found to be highly determined by the level of bio-encapsulation, the carotenoid hydrophobicity, being lower for lycopene than for β-carotene, was the main factor influencing the transfer from the oil into the micelles. Overall, the incorporation into the micellar fraction represents the critical step for carotenoid bioaccessibility. Moreover, the effect of thermal treatments on these systems depended on carotenoid species, being negative for lycopene and positive for β-carotene.

Inactivation of polyphenoloxidase by pulsed light.

The effect of pulsed light on the inactivation of polyphenoloxidase (PPO) in model solutions was investigated focusing on the effect of enzyme concentration and total energy dose of the treatment. PPO inactivation increased with the dose of the treatment. Complete enzyme inactivation was achieved by pulsed light doses higher than 8.75 J cm(-2) . At low PPO concentrations (4 to 10 U), the enzyme resulted highly inactivated by pulsed light treatment. Further increase in enzyme units determined a progressive decrease in PPO inactivation. The latter was attributed to protein structural modifications including cleavage and unfolding/aggregation phenomena. PPO amounts higher than 10 U probably favoured enzyme conformations that were less prone to intermolecular rearrangements leading to inactivation.

Role of structural barriers for carotenoid bioaccessibility upon high pressure homogenization

A specific approach to investigate the effect of high pressure homogenization on the carotenoid bioaccessibility in tomato-based products was developed. Six different tomato-based model systems were reconstituted in order to target the specific role of the natural structural barriers (chromoplast substructure/cell wall) and of the phases (soluble/insoluble) in determining the carotenoid bioaccessibility and viscosity changes upon high pressure homogenization. Results indicated that in the absence of natural structural barriers (carotenoid enriched oil), the soluble and insoluble phases determined the carotenoid bioaccessibility upon processing whereas, in their presence, these barriers governed the bioaccessibility. Furthermore, it was shown that the increment of the viscosity upon high pressure homogenization is determined by the presence of insoluble phase, however, this result was related to the initial ratio of the soluble:insoluble phases in the system. In addition, no relationship between the changes in viscosity and carotenoid bioaccessibility upon high pressure homogenization was found.

Enzymatic cell wall degradation of high-pressure-homogenized tomato puree and its effect on lycopene bioaccessibility.

BACKGROUND High-pressure homogenization disrupts cell structures, assisting carotenoid release from the matrix and subsequent micellarization. However, lycopene bioaccessibility of tomato puree upon high-pressure homogenization is limited by the formation of a process-induced barrier. In this context, cell wall-degrading enzymes were applied to hydrolyze the formed barrier and enhance lycopene bioaccessibility. RESULTS The effectiveness of the enzymes in degrading their corresponding substrates was evaluated (consistency, amount of reducing sugars, molar mass distribution and immunolabeling). An in vitro digestion procedure was applied to evaluate the effect of the enzymatic treatments on lycopene bioaccessibility. Enzymatic treatments with pectinases and cellulase were proved to effectively degrade their corresponding cell wall polymers; however, no further significant increase in lycopene bioaccessibility was obtained. CONCLUSION A process-induced barrier consisting of cell wall material is not the only factor governing lycopene bioaccessibility upon high-pressure homogenization.

Effect of pulsed light on structure and immunoreactivity of gluten

The effect of pulsed light (from 1.75 to 26.25Jcm(-2)) on selected properties of wheat gluten powder and aqueous suspension (absorbance, particle size and microstructure, free sulfhydryl content, protein fractions, protein electrophoretic mobility and immunoreactivity) was investigated. Gluten photoreactivity was strongly affected by hydration. While minor photo-induced structure modifications were observed in gluten powder, pulsed light induced the development of browning and promoted partial depolymerisation of hydrated gluten proteins by disulphide exchange. These changes were associated with a significant decrease in immunoreactivity, suggesting that pulsed light could be exploited to efficiently modify structure and thus functionality of gluten.

Carotenoid bioaccessibility and the relation to lipid digestion: A kinetic study

The micellar incorporation of carotenoids (lycopene, α- and β-carotene) and lipid digestion products (free fatty acids, FFAs, and monoacylglycerides, MAGs) during in vitro digestion of oil-in-water emulsions was investigated by a kinetic approach. A fractional conversion model could adequately describe the hydrolysis of triacylglycerides, formation of FFAs and MAGs, and micellar incorporation of carotenoids, FFAs and MAGs. The release of FFAs and MAGs from TAGs proceeded faster than their incorporation into micelles. Rate constants of carotenoid micellar incorporation were inversely proportional to their hydrophobicity and dependent on the isomeric configuration, being the incorporation of the cis faster than their all-trans isomers. Furthermore, a positive linear relation was found between the micellar incorporation of carotenoids and lipid digestion products. The isomeric form of carotenoids did not affect such relation. The present kinetic approach can be useful to gain mechanistic insight into carotenoid bioaccessibility as affected by various process- and product-related factors.