Wasted Bread as Substrate for the Cultivation of Starters for the Food Industry

Abstract

The amount of bread wasted daily worldwide, throughout its entire lifecycle, from production to distribution, is estimated to be hundreds of tons, therefore representing both economic and environmental issues. This work aimed at the valorization of wasted bread, setting-up a protocol for obtaining a growth medium to be used for the cultivation of food industry microbial starters. The optimization of the protocol included the set-up of parameters for the hydrolysis of the bread nutrient compounds with proteolytic and amylolytic enzymes and the supplementation with nitrogen and/or carbon sources. The suitability of the optimized medium for the growth of lactic acid bacteria, yeasts and fungi from dairy, bakery, and wine industries was assessed. Lactic acid bacteria growth was strongly affected by the quantity and quality of nitrogen sources employed, while yeasts and fungi growth exceeded that obtained with the reference media commonly employed for their cultivation. Wasted bread medium (WBM) represents a realistic option for the valorization and re-use of bread waste, responding to the modern vision of circular economy.

Keywords: bread waste; fungi; growth medium; lactic acid bacteria; starters; yeasts.

FIGURE 1

Concentration of glucose, peptides and amino acids (g/l) of the media obtained from wasted bread (Left axis). Dots represent the distribution of the optical density (A_{620 nm}) values of Lactobacillus plantarum LB1 and Saccharomyces cerevisiae E10 after 24 h of incubation at 30°C in the experimental media (Right axis). Dotted lines indicate the growth of the same strains in reference media, MRS (blue) and Sabouraud (red) for LAB and yeasts, respectively. Experimental media (M₁ to M₄₄) correspondence is reported in Table 1.

FIGURE 2

Flowchart of the protocol for the production of wasted bread medium (WBM).

FIGURE 3

Box-plot showing the distribution of 33 LAB strains based on the parameters of the kinetics of growth: cell density variation between inoculation and the stationary phase (A), maximum growth rate (B), and length of the lag phase (C).

FIGURE 4

Effect of chemical preservatives, calcium propionate (CaP) and potassium sorbate (Ksor), on the growth of Penicillium roqueforti DPPMAF1. Concentrations corresponding to the 25, 50, 75, and 100% of that maximum allowed by the current legislation for baked goods were added to the wasted bread medium (WBM). PDA was used as control medium. Data are the means of three independent analyses. Error bars indicating the standard deviation are represented. ^a–cValues with different superscript letters differ significantly (P < 0.05).

FIGURE 5

Three-dimensional surface plot of the interaction of glucose and peptides and amino acids concentration (g/l) on the growth of Lactobacillus plantarum LB1 (A) and Saccharomyces cerevisiae E10 (B).