Combining untargeted, targeted and sensory data to evaluate food quality changes during storage. A case study on shelf-stable strawberry juice
Nowadays, consumers are paying a lot of attention towards the quality characteristics of food products (e.g. colour, aroma, taste). Upon storage of a food product, its quality characteristics are continuously evolving. A serious decrease in the quality of food products can have a drastic impact on product acceptability by consumers and will result in a food product not being consumed even before the shelf-life date has been reached. To ensure that the quality of a food product can be maintained long enough, knowledge on quality changes during storage is required. This information can be obtained performing analytical (untargeted and targeted) as well as sensorial tests, by the integration of these data and by the application of different data analysis methods. The application of such an integrated approach can be of high value for food quality investigations and shelf-life assessment.
The aim of this work was to develop and evaluate the potential of such an integrated approach for food quality evaluations and shelf-life assessment. In this work, the suggested integrated approach was applied in a case study on pasteurised strawberry juice, being representative for shelf-stable high acid food products. Specifically for the research matrix, this work aimed at gaining quantitative insight into the impact of three storage factors (storage time, storage temperature and oxygen availability) on colour and flavour changes during storage using an integrated approach, which combined untargeted, targeted and sensorial data and different data analysis techniques. To reach the objective, pasteurised strawberry juice was stored at ambient (20 °C) and accelerated temperatures (28, 35 and 42 °C) in two types of PET bottles with a different oxygen permeability.
Different colour-related attributes (redness, total colour difference, chroma, hue angle, anthocyanin and ascorbic acid content) changed significantly during storage at all conditions. Higher storage temperatures and a higher oxygen availability resulted in a faster change of the colour-related attributes as shown by the estimated kinetic parameters (reaction rate constants and activation energy). The observed change in colour of the strawberry juices could be explained by the loss of red anthocyanin pigments and the formation of brown-coloured compounds by the degradation of ascorbic acid.
Flavour changes were studied at three levels. An untargeted fingerprinting approach showed that the volatile fraction of strawberry juice was clearly changing during storage at ambient conditions in both bottle types. The volatiles changing the most during storage at ambient conditions in both bottles could be classified as esters, aldehydes, terpenes, sulfur compounds and ketones. To gain further insight, twelve characteristic aroma compounds were quantified during storage at ambient and accelerated temperatures using a targeted approach followed by kinetic modelling. The estimated reaction rate constants showed that all characteristic aroma compounds changed significantly during storage at each temperature. The rate of change in some compounds was accelerated by storage at higher temperatures. Based on the outcome of the two analytical approaches, it was concluded that a difference in oxygen availability had no significant effect on the rate of volatile changes and that the change in selected aldehydes, terpenes, sulfur compounds and acids was accelerated during storage at higher temperatures. Moreover, it was concluded that the effect of oxygen availability (which was linked to the type of bottle) on volatile/aroma changes was less pronounced compared to its role in colour changes. The observed changes in strawberry juice volatiles caused sensorial differences between non-stored and 20 °C stored samples as shown by the sensory evaluations and odour activity values.
As consumers are the last stage in the food chain, the impact of colour and aroma changes during storage on the acceptability of strawberry juice was also evaluated. The colour- and aroma-based acceptance tests showed that colour changes of strawberry juice are shelf-life limiting. Aroma changes could be noticed by the human senses, however, they will not be critical for the shelf-life of strawberry juice. The colour-based acceptability decreased at all temperatures. A faster decrease in colour-based acceptability was observed during storage at accelerated temperatures. The colour-based shelf-life was reached in the early stages of storage and was shortened at higher temperatures. Analytical cut-off values for the colour-based shelf-life were estimated for each storage temperature relying on the estimated kinetic parameters. These values can be of great value for food industries as they can be used as an indicator for a product’s shelf-life without the need to perform time consuming acceptance tests.
The results of this work demonstrate the applicability of an integrated approach for quality investigations and shelf-life assessment. By combining analytical (untargeted and targeted) and sensorial tests and different data analysis methods, a profound insight into quality changes during storage can be obtained. Based on the results of this work, it is noteworthy to highlight the importance of sensory tests in quality investigations and shelf-life assessment. The application of accelerated shelf-life testing (in this case storage at temperature abuse conditions) showed the negative effect of storage at abuse conditions. In addition, it allows to obtain a faster insight into food quality changes and to predict the rate of quality deterioration at ambient conditions using kinetic models. The latter is useful for shelf-stable food products with a long shelf-life. Lastly, the use of different data analysis methods (kinetic modelling, chemometrics and survival analysis) is recommended in an integrated approach.