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Digital archive of theses discussed at the University of Pisa

 

Thesis etd-02012024-102030


Thesis type
Tesi di dottorato di ricerca
Author
BIANCHI, ALESSANDRO
URN
etd-02012024-102030
Thesis title
Evaluation of food shelf-life combining chemical-physical, sensory and non-destructive analyses
Academic discipline
AGR/15
Course of study
SCIENZE AGRARIE, ALIMENTARI E AGRO-AMBIENTALI
Supervisors
tutor Dott.ssa Sanmartin, Chiara
Keywords
  • bread
  • e-nose
  • olive oil
  • primary shelf-life
  • secondary shelf-life
  • wine
Graduation session start date
23/02/2024
Availability
Withheld
Release date
23/02/2094
Summary
The concept of shelf-life is fascinating because it combines problems with a scientific basis with economic, government, and consumer-related ones. These latter factors are dynamic and subject to change in response to changes in society, particularly in terms of preferences and requirements. Due to this, there is not a standard, widely accepted definition of product shelf-life. This is especially true for the food industry, where businesses commonly create their own shelf-life assessment methods with sometimes dubious scientific foundations since there is a lack of a comprehensive and unified perspective on the shelf-life issue, as well as accessible and economical approaches. It is worth underlining that food quality, defined as an assemblage of a huge number of properties affecting the degree of food acceptability, is a dynamic state continuously moving to reduced levels. It implies that for any kind of food product there should be a defined quality level discriminating products that are still acceptable for consumption from those no longer acceptable.
This work present shelf-life studies applied on different food matrices (bread, wine and olive oil) using combined analytic techniques (physical-chemical, sensory e non-destructive analyses). The first section of the work is focalized on the Primary shelf-life (PSL) and the Secondary shelf-life (SSL) of bread and reported 3 studies: (i) Effect of modified atmosphere packaging (MAP) on the PSL of sourdough bread (PDO Tuscan bread); (ii) Effect of fertilization regime (N/P kg/ha) of common wheat on flour quality and PSL of PDO Tuscan bread; (iii) Effect of formulation (flour and leavening agent) and modified atmosphere packaging conditions on the PSL and SSL of bread. The second section is focalized on the SSL of wine and reported 2 studies: (i) Impact of different packaging and capping systems on the SSL of white wine; (ii) Effect of different packaging strategies on the SSL of young and structured red wine. The last section reported a study on the application a non-destructive technique (electronic nose) for the olive oil, focusing on the estimation of fruity aroma level of different Spain origin olive oils.
Considering the first section of the thesis, the results about the application of MAP on bread storage, showed that pure gases (CO2, N2, Ar) displayed good qualities as storage atmospheres compared to Air. Besides, both Mix CO2/N2 and Mix CO2/Ar were the best in slowing down the staling process, thus doubling the shelf-life of bread, compared to other atmospheres; however, the sensory acceptability of sourdough bread was lower due to the higher acidity perception. In conclusion, Argon, as a preservation atmosphere, seems to be the best solution to extend the shelf-life of PDO Tuscan bread.
The results of fertilization regime (Nitrogen/Phosphorus) showed that the most significant influence on shelf-life was related to the different fertilizations of wheat. In fact, when N was present in equal dose to P (90/96 or 45/48 kg/ha) or slightly higher (90/48 kg/ha), the bread tended to last longer over time. Instead, when these ratios were unbalanced in favor of N (135/48 or 135/96 kg/ha) and in favor of P (45/96 kg/ha), the shelf-life decreased considerably.
The final results showed how the leavening agent used has the major effect on the PSL of breads, especially in combination with the gas used in the package. Compared to Air, Ar combined with sourdough reduces water loss, slows down the staling process and allows bread to have a longer shelf-life, preserving its initial characteristics. This effect did not occur for bread made with baker's yeast, for which it might be useful to use a different MAP. Indeed, for the SSL, the only effects detected are related to the leavening agents, with a longer shelf-life of sourdough breads compared to the baker’s yeast ones. Our results showed a strong effect related to the formulation of bread, regardless the storage conditions, on both PSL and SSL. Furthermore, we can conclude that the parameters of weight decrease and water activity, which can be easily and quickly measured, combined with sensory analysis can be used as markers to assess the PSL and SSL of bread.
Regarding the section devoted to wine shelf life, both white and red wines were monitored during storage into different packaging systems (polymeric cap, screw cap, natural cork, crow cap, and Tetra Brik) and our results suggest that the kinetic constant (k𝒄) for the total SO2 degradation and the evolution of the sensory acceptability (HI) can be used as valid tools to study the evolution of the SSL on wine. The polymeric stopper proved to be the best for storing wine when single or repeated cycles operations of opening and closing of bottle were carried out. These results are due to the technical characteristics of the polymeric material, which tends to vary to a limited extent in its shape, also after repeated solicitations (low susceptibility to deformations, lacerations, oxygen tightness).
During the third part of the research, the e-nose was applied to the quality assessment of olive oil, focusing on the fruity level, which is strongly affected by storage conditions. The results obtained, considering the variability of the samples, showed a value of Mean Average Error (MAE) which is below 0.88 in all the cases. In particular, the MAE of 0.67 obtained for variety (cv. Picual), and the similarity in the models fitted show the robustness of the approach and the applicability of the methods. The utilization of a large number of samples or of a specific models for variety allows to construct prediction models based on e-nose data that provide useful results for this application. Finally, the application of e-nose to rapid detection of the fruity aroma could be a valid tool to monitor the evolution of the quality during the shelf-life of olive oils.
In conclusion, the work highlighted that the study of the shelf-life of food products is very complex because each product has a different degradation rate correlated to formulation, storage conditions, packaging atmosphere and also each product has a specific acceptability limit, defined according to its peculiar qualities.
A combined approach, based both on physical-chemical and sensory markers, can be a valid tool to define the primary or secondary shelf-life of foods. In addition, the pairing with a non-destructive technique such as the electronic-nose, could be a suitable approach to deeply monitor food stability and then assess shelf-life.
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