C. R. Lerici

Review of non-enzymatic browning and antioxidant capacity in processed foods ☆

Browning reactions represent an interesting research area for the implications in food technology, nutrition and health. The development of some non-enzymatic browning reactions, such as Maillard reaction, has been recently associated to the formation of compounds with strong antioxidant capacity. In this paper, the relation between colour changes due to non-enzymatic browning and the formation of compounds with antioxidant activity is discussed. Simple positive or complex correlation between colour and antioxidant properties can be found depending on composition and technological history of the product. Complex relations between these variables are generally obtained in multi-component and in formulated foods, where the simultaneous development of a number of reactions, interacting or prevailing Maillard reaction itself, can affect in opposite ways the overall antioxidant properties and colour of the product.

Loss and/or formation of antioxidants during food processing and storage

It is well known that natural antioxidants contained in foods are significantly lost during processing. Nevertheless it was recently demonstrated that thermal treatments can induce the formation of compounds with new antioxidant properties. This is the case of the Maillard reaction products (MRPs) whose presence as well as their potential effects have been scarcely investigated. In the present work the loss of natural antioxidants in relation to processing and the formation of MRPs with antioxidant activity were studied in different food systems such as tomato derivatives and coffee. Results showed that, although the concentration of natural antioxidants was significantly reduced as a consequence of the thermal treatments, the overall antioxidant properties of the food products were maintained or even enhanced by the development of MRPs.

Antioxidant properties of tomato juice as affected by heating

The changes in the overall antioxidant properties of tomato juice samples and model solutions as a consequence of heat treatments were studied. The antioxidant properties were evaluated both through the measurement of the chain breaking and the oxygen scavenging activities. While a decrease in the antioxidant potential was found for short heat treatments, a recovery of these properties was measured by prolonging heating times. Results suggested that the initial reduction in the overall antioxidant activity can be attributed not only to the thermal degradation of naturally occurring antioxidants but also to the formation of early Maillard reaction products (MRP) with pro-oxidant properties. The gain in antioxidant activity coincided with the formation of brown MRP. © 1999 Society of Chemical Industry

Effects of drying processing on the Maillard reaction in pasta

The effect of low, high and very high drying temperatures on the development of the Maillard reaction in pasta was studied. In particular, an investigation was carried out into the influence of the different temperatures used on the development of colour, the formation of furosine and the changes in the chain breaking activity of pasta samples having different moisture contents as well as on the adsorption and desorption isotherms. Results showed that, depending on temperature, time and moisture conditions, pasta had antioxidant or pro-oxidant properties. The increase in the antioxidant potential was always associated with an increase in brown colour, while the pro-oxidant properties were observed in the early stages of the Maillard reaction.

Effect of maillard reaction volatile products on lipid oxidation

Maillard reaction volatile compounds (MRV), prepared by heating a glucose-glycine solution, were tested as antioxidants in soybean oil (SBO) thermoxidation. The volatiles were transferred into the oil by stripping with a stream of Nitrogen and substituting the atmosphere above the oil with air containing MRV. Standard accelerated oxidation was performed by heating the SBO. Peroxide value measurement and headspace gas Chromatographic analysis were carried out on all the samples. The MRV antioxidant activity was evaluated by determining the effect of the induction period and the kinetic rate constant of peroxide and oxidation volatiles formation. The MRV showed a significant antioxidant activity. The effectiveness was variable depending on MRV transfer method to the oil, and the Maillard reaction extent was related to the browning level of glucose/glycine solution. It was found that the maximum effect of MRV prolonged about three times the induction period and reduced the kinetic rate constant by half in relation to the control sample. MRV affects oxidative stability of soybean oil by lengthening the induction period as well as by decreasing the rate of oxidation at the propagation state and reducing the formation of hexanal.

Interaction between Maillard reaction products and lipid oxidation in starch-based model systems

The effect of Maillard reaction products (MRPs) on the kinetics of lipid oxidation in intermediate-moisture model systems containing pregelatinised starch, glucose, lysine and soybean oil has been studied. The samples, either containing all components or excluding one or more of them, were heated at 100 °C for different times. Lipid oxidation and browning indices were measured and the results confirmed the ability of MRPs to retard peroxide formation. Under the conditions adopted, the rate of the Maillard reaction was increased by the presence of the oil and its oxidation products. The antioxidant action of MRPs was also evaluated using a peroxide-scavenging test based on crocin bleaching. The results demonstrated that antioxidant activity developed with increased browning of the samples.

Ethanol vapour pressure as a control factor during alcoholic fermentation

Aqueous solutions of glucose/fructose mixtures with varying concentrations of ethanol were used to study the effects on fermentation of ethanol vapour pressure and water activity. Water vapour pressure was found to increase significantly with temperature in the range 15 to 30‡C. The effects on glucose fermentation bySaccharomyces cerevisiae Bg7FL of the variables glucose concentration, Tween 80 concentration, temperature and ammonium and ethanol concentrations were examined using central composite design. A best fit equation describing the main, quadratic and interactive effects of the five variables on yeast growth rate was produced. Further model systems were analysed in which the effects of ethanol vapour pressure, water vapour pressure and ethanol concentration on maximal growth rate of the yeast strain were studied. Above 18‡C, neither ethanol concentration nor ethanol vapour pressure controlled the fermentation rate. Ethanol toxicity was shown to be associated with its vapour pressure rather than its concentration.

Hygrometric measurements for the evaluation of the stability of model food emulsions

Abstract A non-destructive test is proposed, based on the measurement of the change in the relative humidity (%RH) needed to reach the equilibrium value (%ERH), which makes a comparative evaluation of the degree of dispersion between the aqueous and lipidic phase and the stability of emulsions. By measuring the rate to reach the %ERH, a kinetic index ( k ) has been introduced, describing the ‘resistances’ to the mass transport (water vapour) from the bulk emulsion to its surface and to the head space of the sample cell. To define this index a model of water adsorption to the gas-liquid interface of the bulk emulsion is described. The model is based on a formalism similar to that used to describe a Langmurian kinetic. In oil-in-water emulsions the destabilising processes (creaming, coalescence) during storage are implied in the formation of a ‘barrier’ which block the aqueous vapour or decrease the rate at which it comes to the surface. Thus, the corresponding k value of the model tends to decrease, and the decrease is higher for the more destabilised emulsified system. In the water-in-oil dispersed systems, the k index is able only to describe the degree of dispersion and partly loses the ability to indicate changes that take place in the bulk system with time.

2.14 – Evaluation of Ethanol Activity in Food and Drink for Studying the Adverse Effects of Ethanol on Human Health

It is generally recognised that excessive alcohol consumption is a causative factor in several diseases. In general, risk and damage are considered a function of the amount of alcohol consumed, while ‘how’ alcohol is consumed is rarely considered. In this paper, ethanol vapour pressure of model systems and of some widely consumed alcoholic beverages was measured in order to demonstrate that the effects of ethanol could be better described in terms of the physicochemical properties of ethanol, such as ethanol activity and ethanol vapour pressure, rather than of the sole ethanol content. A gas-chromatographic method for measuring the ethanol vapour pressure and activity in food and drink, is also briefly described. In addition, vapour-liquid relationships are also discussed.