Monitoring the metabolite content of seasoned zucchinis during storage by NMR-based metabolomics

Abstract

This study applied ¹H NMR metabolomics to monitor the metabolite content of baked and seasoned zucchinis packaged in both compostable and plastic trays. Polar extracts of samples stored at 4 °C up to 35 days were investigated to check for metabolite changes upon shelf life. The evolution of the integral values of only the main metabolites responsible for sample differentiation (lactate, acetate, malate, α and β glucose and sucrose) were further analysed and compared. In particular, the evaluation of lactate and acetate amount, considered markers of fermentation progress, showed a comparable performance for the two types of packaging in preserving the freshness of seasoned zucchinis, confirming the maintenance of food product composition within the declared shelf life period in the recommended storage conditions. Albeit preliminary, the results support the NMR metabolomics as a tool for identifying candidate metabolites to monitor the shelf life of foods, thereby improving the understanding of molecular changes during storage.

Keywords: Metabolite; NMR; Packaging; Shelf life; Zucchini.

Fig. 1

Representative ¹H NMR spectrum of polar extract of baked and seasoned zucchinis (A) with the expansion of aliphatic (B) and aromatic (C) regions. The assignments of the main metabolites are reported.

Fig. 2

Score scatter plot (A) and loading plot (B) of PCA performed including all zucchinis analysed of 1st sampling (February 2021) with the exclusion of 31P and 35P resulted strong outliers. Green filled circles, and red diamonds represent zucchinis packaged in compostable and plastic trays, respectively. The main metabolites responsible of samples differentiation are highlighted in the loading plot. (For interpretation of the references to colour in this figure legend, the reader is referred to the Web version of this article.)

Fig. 3

Score scatter plot (A) and loading plot (B) of PCA performed considering all zucchinis of 1st sampling (February 2021) packaged in compostable trays. Samples stored up to 22 days are highlighted by dotted line. The main metabolites responsible of samples differentiation are highlighted in the loading plot.

Fig. 4

The evolution of the main metabolites responsible of samples differentiation considering zucchinis of 1st sampling packaged both in plastic (red diamonds) and compostable (green filled circles) trays during storage, are reported. Particularly, the evolution of integrals values of buckets included lactate (bucket at 4.04 ppm, A), acetate (bucket at 1.90 ppm, B), malate (bucket at 4.25 ppm, C), α-glucose (bucket at 5.17 ppm, D), β-glucose (bucket at 4.58 ppm, E), and sucrose (bucket at 5.38 ppm, F) are reported. (For interpretation of the references to colour in this figure legend, the reader is referred to the Web version of this article.)

Fig. 5

Score scatter plot (A) and loading plot (B) of PCA performed considering zucchinis of both 1st (green filled circles) and 2nd (blue triangles) sampling packaged in compostable trays. The main metabolites responsible of samples differentiation are highlighted in the loading plot. (For interpretation of the references to colour in this figure legend, the reader is referred to the Web version of this article.)

Fig. 6

The evolution of the integrals values of buckets including lactate (bucket at 4.04 ppm, A), and acetate (bucket at 1.90 ppm, B) during the storage of zucchinis packaged in compostable trays of 1st sampling (green filled circles) and 2nd sampling (blue triangles) are reported. (For interpretation of the references to colour in this figure legend, the reader is referred to the Web version of this article.)