**10. Co-ensiling forage with food processing waste and TMR conservation**

Food processing residues represent high-energy organic material already used in some way that could include either food-processing residues from food industries or distiller's grains from the ethanol production. These residues could easily be used by farms closely located to the production site, but their relatively high humidity content renders them prone to a rapid deterioration. New ensiling techniques allow mixing them with low moisture forage or grain in order to perform a fermentation that is enclosed in a kind of total mixed ration (TMR) acidic conservation.

Aiming to use a bakery co-product waste, Rezende et al. [75] tested possibilities of re-hydration, treating it with acid whey or water and levels of urea. The authors found that the resulting silages had reduced populations of molds and yeast by acidification process. However, the initial population of these microorganisms was high, mainly accounting of *Penicillium* and *Aspergillus* spp. Inoculating with a bacteria that could produce antifungal chemicals, including acetic and propionic acids, might be considered for this kind of co-product.

TMR silage is an important source of ruminant feed. This practice has been more common in some places, where companies or producers mix wet co-products with dry feeds to prepare TMR that is then preserved as silage. Based on conventional criteria, aerobic deterioration could occur easily in TMR silage, because lactic acid prevails during fermentation and any sugars remaining unfermented can serve as substrates for the growth of yeasts. However, some trials [76, 77] have been shown that when added concentrate, the brewer's grains or soybean curd residue, the main co-products used in TMR preserved do not show heating in the TMR. For the trial with brewers' grain-based TMR, the main bacteria found in the stable silages were *L. buchneri*, but for the soybean curd-based TMR, the main LAB found were *P. acidilactici* and *L. brevis* [78], showing potential association of those bacteria

*New Advances on Fermentation Processes*

ments from the different metabolites.

geographical regions and over time are nonexistent.

microbial communities in silage is recent. McAllister et al. [12] published a review providing a technological and methodological overview. Currently, the number of trials performed using this technique is small enough that repetitions between

Amplicon-based metasequencing represents the entry level of the -omic techniques. For silage research, the industry could also consider metagenomic, proteomic, transcriptomic, or epigenomic as a potential area of study. A review of the possibilities offered by metabolomics in agriculture was recently published [70]. Since ensiling is based on the fermentation of forage crops, knowledge of the metabolic activity of the forage prior to ensiling would be useful. A review by Rasmussen et al. [71] provides an insight into how plants are coping with physiological changes due to breeding strategies, associations with endophytes or rhizobia, responses to nutrients, and, more interestingly, on the metabolic responses to the osmotic stress. Harvesting and wilting will directly influence plant cell activities and nutrient cycling. The authors reported that amino acids, fatty acids, and phytosterols generally decrease following the water stress, while sugars and organic acids increased. Since the fermentation process requires fermentable sugars for optimal acidification of the forage, wilted plants may respond positively toward ensiling. We need to consider the speed of those changes in concentration of metabolites during wilting compared in order to propose a model of the response to an osmotic stress. Ould-Ahmed et al. [72] provided some knowledge on this response to wilting while studying changes in fructan, sucrose, and some associated hydrolytic enzymes, concluding there is a positive effect toward ensiling require-

Metabolomic profiling of silage was performed in a study aiming to understand the role of inoculation with *L. plantarum* or *L. buchneri* in alfalfa silage against a noninoculated control [13]. The authors were able to distinguish all three inoculation treatments by a PCA of the 102 metabolites surveyed. The major metabolites observed were related to amino acids, organic acids, polyhydric alcohols, and some derivatives. One of the main observations was an increase in free amino acids and 4-aminobutyric acid following the inoculation with *L. buchneri* and a decrease in

Testing the same two LAB strains on whole plant corn silage instead of alfalfa, Xu et al. [32] observed a total of 979 chemical substances, from which 316 were identified and quantified. The PCA allowed separating the three inoculation treatments along the first axis, representing nearly 80% of the variations between samples. The second axis was able to further distinguish how inoculation with *L. buchneri* influenced the fermentation. Inoculation with either *L. plantarum* or *L. buchneri* contributes to increase the concentration of amino acids and phenolic acids, 4-hydroxycinnamic acid, 3,4-dihydroxycinnamic acid, glycolic acids, and other organic acids. Inoculation with *L. buchneri* also induces higher concentration of 2-hydroxybutanoic acid, saccharic acid, mannose, and alpha-d-glucosamine-1-phosphate, among others. Other substances were increased by ensiling without specific impact of the inoculants, such as catechol and ferulic acid that could have

Metabolomic studies can also be used in defining a metabolomic signature specific of different forage and silage on feed efficiency of ruminants. With the aim of identifying feed efficiency traits in beef cattle, Novais et al. [73] investigated how serum metabolomic profiles could be used to predict feed intake and catabolism. They identified different molecules having feed efficiency role. Two molecules from the retinol pathway, vitamin A synthesis, were significantly associated with feed efficiency (higher concentration of retinal and lower concentration

cadaverine and succinic acid following the inoculation with *L. plantarum.*

**166**

of retinoate).

antioxidant functions.

to preserve TMR silages. A similar trial was performed by Ferraretto et al. [79] to test how the process influenced luminal *in vitro* starch digestibility. They used dry ground corn to adjust the humidity level of wet brewers' grain and observed an increase in digestibility of the starch from the combined feed.

Nishino and Hattori [80] evaluated two bacterium-based additives in wet brewer's grains stored as a TMR in laboratory silos with lucerne hay, cracked maize, sugar beet pulp, soya bean meal, and molasses. The additives tested were the homofermentative LAB, *L. casei*, and the heterofermentative LAB *L. buchneri*. This last one was responsible for controlling yeast growth and the homolactic one helped in the fermentative profile of the ensiled TMR.
