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In the Ecuadorian Amazon region, there is a great potential for agricultural resources, including orito banana, which is produced and harvested throughout the year. The first quality fruits are intended for human consumption, while the thin and small fruit is used in its natural state for feeding animals of zootechnical interest. It is known, from references, that green banana fruits, in their natural state, contain a high content of secondary metabolites, which can exert a negative effect on the use of nutrients by animals, so it is necessary to use processing techniques, such as solid state silage, to take advantage of these resources (Kamrunnessa et al. 2019).
In this sense, previous studies with alternative feeds have shown that through the production of solid silage, protein and antioxidant contents of raw materials can be improved for animal feeding (Salinas et al. 2014). The objective of this study was to determine protein content, total phenols and antioxidant activity of green orito banana (Musa acuminata AA) fruit silage, inoculated with whey, for its application as food for animals.
For silage, waste green orito banana fruit was obtained in Mariscal market, in Puyo city, Pastaza province, Ecuador. Immediately, it was transported for 5 min. to the microbiology laboratory of the Universidad Estatal Amazónica (UEA). Once there, they were washed and ground in a hammer mill, equipped with a blade and a 2-cm screen. A part of the chopped material (2 kg) was collected and transferred to the Bromatology Laboratory of UEA, to determine the content of crude protein (CP), total phenols and antioxidant activity.
The fruit in its natural state had 4.26% CP, 3,888.46 μMol GAE/kg DM of total phenols and 351.85 μMol TROLOX/kg DM of antioxidant activity. Silage was produced with the remaining chopped orito banana, combining raw materials: chopped green orito banana fruit (67%), wheat powder (20%), Pecutrin (0.5%), molasses (2%), calcium carbonate (0.5%) and fresh whey (10%). Mixing lasted 5 min., as homogeneous as possible, and was introduced into 18 polyethylene microsilos, with a capacity of 1 kg each. Three microsilos were evaluated for each conservation time (0, 1, 4, 8, 15 and 30 d).
CP determination was carried out by Kjeldahl method. Total phenols, in gallic acid equivalent (GAE), were determined according to Folin-Ciocalteau, and antioxidant activity in TROLOX by FRAP (2,4,6-tripyridyl-s-triazine). The analyzes were carried out by triplicate at the UEA bromatology laboratory. Analysis of variance was performed and Duncan (1955) test (P <0.05) was applied for comparison of means. All analyzes were carried out with Infostat statistical program, version (2012) for Windows.
Table 1 shows CP contents, total phenols and antioxidant activity of orito banana fruit silage. The highest protein values were achieved on days 4, 8, 15 and 30, without significant differences among them, and they were superior (P <0.05) to days 0 and 1. Regarding content of total phenols, fermentation presented the highest value (P <0.05) on day 30, while day 0 had the lowest one. As to the antioxidant activity, the best value (P<0.05) was obtained on day 15, and the lowest result was obtained at day 0.
Table 1 Content of crude protein, total phenols and antioxidant activity of ensiled orito banana fruit
| Variables | Days of fermentation | SE ± | P value | |||||
|---|---|---|---|---|---|---|---|---|
| 0 | 1 | 4 | 8 | 15 | 30 | |||
| CP, % | 7.86c | 11.61b | 15.54a | 15.44a | 15.41a | 15.33a | 0.04 | P=0.0001 |
| Total phenols, μMol GAE/kg DM | 12781.73e | 14571.43d | 16544.61c | 16952.19c | 25442.85b | 35812.85a | 53.48 | P=0.0001 |
| Antioxidant activiy, μMol TROLOX/kg DM | 410.55e | 515.87d | 576.47d | 692.04c | 3034.98a | 1636.11b | 3.28 | P=0.0001 |
abcdeDifferent letters in a row differ at P<0.05, according to Duncan (1955)
The greatest increase of silage protein with respect to fermentation time, is related to the increase of microbial mass in the substrate (Yunus et al. 2015). In this study, fresh milk serum was used as inoculum source, which is rich in Lactobacillus sp. and Enterococcus sp. (Martínez-López et al. 2016). In this regard, Gunawan et al. (2015) carried out a research with cassava meal, fermented with Lactobacillus, Saccharomyces and Rhizopus as inocula, in which they reported the highest protein content at 120 h post-inoculation, for the material treated with Lactobacillus (from 1.92% in natural meal to 8.58% in fermented material). Khan et al. (2018) observed that fermentation reduces the content of bitter free amino acids (phenylalanine, tyrosine and leucine), and increases amino acids with antioxidant potential (taurine, aspartic acid, cysteine, thiazolin cysteine and γ-amino-butyric acid).
Regarding the increase of polyphenol content of the ensiled material during the fermentation time, Dey et al. (2016) stated that this is due to the use of the starter culture of lactic acid bacteria through fermentation process. Antioxidant phenolics are produced by microorganisms through a metabolic pathway through extracellular enzymatic action, which increases their concentration in the substrate.
The fermented material on day 15 showed the highest antioxidant activity, which was partially reduced on day 30 of evaluation. Guan et al. (2020) stated that lactic acid bacteria in the silage show an optimal activity until day 14, which later tends to reduce in the substrate. The best antioxidant activity in fermented foods of plant origin is related to the rupture of ester bonds in free phenolic compounds, due to the action of lactic acid bacteria with a probiotic effect. Hole et al. (2012) evaluated the bioavailability of phenolic acids in whole barley and oat meals, after fermentation with three probiotic strains (Lactobacillus johnsonii LA1, Lactobacillus reuteri SD2112 and Lactobacillus acidophilus LA-5) of lactic acid bacteria. These strains exhibited maximum increases in free phenolic acids, from 2.55 to 69.91 μg g -1 DM and from 4.13 to 109.42 μg g-1 DM, in whole barley and oat, respectively.
In a study conducted by Khan et al. (2018) on dry pulp of Dimocarpus longan, it was demonstrated that, through fermentation, an increase of 17.4% in the amount of free phenolic content was achieved. Also, the phenolic composition, determined by HPLC, revealed significant changes in the content of free gallic acid (37.9%) and 4-methylcatechol (25.7%). Similarly, fermentation improved ferric reducing antioxidant power (18.3%), absorption capacity of free and total radicals (11.8%), and free phenolic fraction (37.4%), respectively. Finally, phenolic acids, released by the enzymatic action of lactic bacteria, constitute antioxidant peptides to formulate functional and nutraceutical foods for humans and animals.
It is concluded that, through fermentation process of the waste green orito banana fruit, between 0 and 30 days, the best protein content and antioxidant activity were achieved at 15 days. Therefore, a food with potential for animal health was achieved.
