Amino acid, mineral, condensed tannin, and other chemical contents of olive leaves (Olea europaea L.) processed via solid-state fermentation using selected Aspergillus niger strains

Abstract

Altop, I. Coskun, G. Filik, A. Kucukgul, Y.G. Bekiroglu, H. Cayan, E. Gungor, A. Sahin

and G. Erener. 2018. Amino acids, minerals, condensed tannin, and other chemical contents

in olive leaves (Olea europaea L.) processed via solid-state fermentation using selected

Aspergillus niger strains. Cien. Inv. Agr. 45(3): 220-230. The present study aimed to examine

the effects of solid-state fermentation (SSF) using selective A. niger strains on the amino acid,

mineral, condensed tannin, and other chemical contents of olive leaves. The dried samples were

divided into nonfermented (C) and fermented (F) olive leaves, and the latter were fermented by

the following A. niger strains: ATCC® 9142TM (F1), ATCC® 200345TM (F2), ATCC® 52172TM (F3),

and ATCC® 201572TM (F4), with three replicates for each treatment. Group F4 presented the best

results, although all fermented groups generally presented higher performance than C. The total

content of amino acids of the fermented olive leaves increased by 68–209% in comparison to

that of C, while the cellulose content of the fermented olive leaves decreased by 7–25%. The ash,

crude protein (CP), and ether extract (EE) contents increased after fermentation, but the crude

fiber (CF) and nitrogen-free extract (NFE) contents decreased. The content of neutral detergent

fiber (NDF) did not change, but acid detergent fiber (ADF) varied among the groups. The starch

and sugar contents of all fermented groups except F1 also decreased compared to those of C.

The mineral contents increased in all fermented groups, and the condensed tannin content varied

according to the A. niger strain used. Thus, olive leaves fermented with different A. niger strains,

especially F4, seem to have considerable potential as ruminant feed, as they are enriched with

amino acids and minerals and have an improved chemical composition. However, these results

should be supported and validated by animal experiments.