Producers are increasingly interested in shelf-life studies to obtain rationalization and optimization of processes, packaging, logistics, as well as the objective definition of legal durability. Let’s take a look in detail.
by Roberta Mastrocinque, Arianna Roda, Milena Lambri*
Institute of Oenology and Food Engineering, College of Agriculture, University Cattolica del Sacro Cuore, Piacenz
The interest of consumers and businesses in shelf-life studies
Consumer demands are increasingly directed towards high-quality food with the expectation that such level could be kept from the time of its purchase to that of its consumption, not only to ensure essential food security, but also to minimize unwanted sensory and nutritional changes. The English expression “shelf-life” which translates the Italian “vita di scaffale”, beyond its literal meaning, indicates the durability of a product in certain storage conditions, and the time limit within which the progress of individual reactive events determines modifications that are, however, undetectable from a sensory point of view, or still acceptable for the food’s safe use. The interest in shelf-life studies by producers is due to the opportunity to obtain rationalization and optimization measures for processes, packaging, logistics, as well as the objective definition of legal durability (expiry date or date of minimum preservation/shelf-life of a packaged product). Therefore it is important for manufacturers to have available data and tools to provide for maximum shelf-life, with relation to certain storage conditions.
The shelf-life of chocolate
In particular, the shelf-life of chocolate depends on a large number of factors, including the presence of a filling or other ingredients, correct tempering, temperature and moisture of storage and material used for packaging. The qualitative characteristics of chocolate, such as its shine, taste, resistance to heat, texture, surface resistance and its characteristic “snap” are primarily influenced by the physical properties of fat, that is cocoa butter. These are also the main causes for abnormal smells, the so-called off-flavors. The oxidation of fat, in fact, leads to the formation of numerous non-volatile and volatile compounds, many of which are important from the point of view of taste, smell and nutrition (aldehydes, ketones and alcohols). It is known, however, that other natural components, such as polyphenols and vitamin E, have a protective and antioxidant role against lipids. Therefore it is important to understand the behavior of a fat, like that of cocoa butter, which is present in semi-finished and finished products, rich in natural protective factors, such as polyphenols and vitamin E, with protective and antioxidant role. In fact, being sources of lipids and sugars and besides having nutritional effect for humans, cocoa and chocolate are also rich in minerals and antioxidant compounds, mainly polyphenols.
The results of a shelf-life study held at the Institute of Oenology and Food Engineering of the University Cattolica del Sacro Cuore of Piacenza about three types of chocolate (dark chocolate, milk chocolate, and gianduja/hazelnut chocolate) indicate, first of all, compliance with microbiological requirements (EC Regulation, 2005 for pastry products) during the sixteen months of storage at 21 ± 2°C temperature and 65% RH. Concerning the evolution of lipid components, monitored every four months starting from their production, the three chocolates have maintained a number of peroxides (fig. 1) corresponding to a good state of preservation (EC Regulation, 1991). In particular, the results showed undetectable peroxides at the time of production (t0), while at t4 time significant increase especially in milk chocolate and dark chocolate has been registered. In gianduja chocolate the number of peroxides is less than the other two chocolates, confirming the observations of other authors who attribute such behavior to phytochemical compounds present in dried fruit, in this case hazelnuts. It should be noted that, as observed for milk chocolate, after sixteen months (Fig. 1) the number of peroxides can suffer a decrease when hydroperoxides are progressing into short chain aldehydes — secondary products resulting from decomposition of the same. This phenomenon can be evaluated through Kreis value test, which consists of a visual detection of short chain aldehydes, which are indicative of early rancidity. The results were negative for each sample and for all analysis, because no red color development was registered (fig. 2). Therefore, even if the analyzed matrices possess high fat content (cocoa butter and hazelnut oil), lipid oxidation is very slow, even after sixteen months storage.From the analysis on polyphenols, made through Folin-Ciocalteu reagent, it is possible to measure the content of not-oxidized water-soluble polyphenols. First of all, a slight increase in dark chocolate and milk chocolate from t0 to t4 time (fig. 3) has been noted, while the content of not oxidized polyphenols remained almost constant in gianduja chocolate until t8 time, by dropping evidently in the remaining period of storage.