Apple Aminoacid Profile and Yeast Strains in the Formation of Fusel Alcohols and Esters in Cider Production

Abstract

The amino acid profile in dessert apple must and its effect on the synthesis of fusel alcohols and esters in cider were established by instrumental analysis. The amino acid profile was performed in nine apple musts. Two apple musts with high (>150 mg/L) and low (<75 mg/L) nitrogen content, and four enological yeast strains, were used in cider fermentation. The aspartic acid, asparagine and glutamic acid amino acids were the majority in all the apple juices, representing 57.10% to 81.95%. These three amino acids provided a high consumption (>90%) during fermentation in all the ciders. Principal component analysis (PCA) explained 81.42% of data variability and the separation of three groups for the analyzed samples was verified. The ciders manufactured with low nitrogen content showed sluggish fermentation and around 50% less content of volatile compounds (independent of the yeast strain used), which were mainly 3-methyl-1-butanol (isoamyl alcohol) and esters. However, in the presence of amino acids (asparagine, aspartic acid, glutamic acid and alanine) there was a greater differentiation between the yeasts in the production of fusel alcohols and ethyl esters. High contents of these aminoacids in dessert apple musts are essential for the production of fusel alcohols and most of esters by aromatic yeasts during cider fermentation.

Free amino acid composition of apple juices with potential for cider making as determined by UPLC-PDA

“…Phenylalanine was the second most abundant amino acid in most of the juices examined, with Rome having the highest proportion of phenylalanine with 49.2 ± 1.0% of the total amino acids, while Enterprise had the lowest proportion of phenylalanine with 4.8 ± 0.06% of the total amino acids. This finding differs from previous reports of phenylalanine representing only a small proportion of the total amino acids in apples, as low as 0.2–0.4% in dessert apples . Trace amounts of phenylalanine were found in British cider apples , and an average of 1.7–4% of the total amino acids was found in Spanish cider apples .…”

“…While the proportions of amino acids observed in a juice sample from a given cultivar may be influenced by growing season , crop load , site, rootstock and other factors , our data provide insight as to the extent of variation for each amino acid, and the ranges of relative concentrations of amino acids that could be expected in apple juice. The predominance of asparagine among all other amino acids was consistent with previous studies , although some prior research also reported threonine being the predominant amino acid (53.4%) in Fuji apple juice and aspartic acid being the major amino acid (41.1%) in Brazilian dessert apples .…”

“…The apples in our study contained a higher proportion of aspartic acid than was reported in a study of six British cider apple cultivars, in which the relative concentration of aspartic acid was 5.88 ± 1.63% on average . The apples in our study contained less aspartic acid compared with Fuji apples grown in China, in which the relative aspartic acid concentration was 26.5 %, and for Brazilian dessert apples, where 41.1% aspartic acid was reported .…”

“…Total amino acid concentration in the juices from 13 cultivars ranged from 18 ± 0.2 mg/L in Blacktwig to 57 ± 0.8 mg/L in Enterprise, with an average of 33 ± 1.5 mg/L. These results are lower than previously reported total amino acid concentrations in Brazilian dessert apple musts (from 192 mg/L to 431 mg/L) , Fuji apples grown in China (617.81 mg/L) , Spanish cider apples (81.39 ± 39.14 mg/L) and British cider apples (average of 63 mg/L for six cultivars) . These differences could be attributable to multiple factors including differences in nitrogen fertilisation practices among growing regions.…”

“…The highest relative concentration of glutamic acid we observed was 9.99 ± 0.005% in Winesap and the lowest was 2.30 ± 0.04% of the total amino acids in Granny Smith. Here, apples contained more glutamic acid than British cider apples, in which the relative concentration of glutamic acid was 1.93 ± 1.48% on average , but much less than Spanish cider and Brazilian dessert apples, which the average relative concentrations of glutamic acid were 13.5% across six cultivars , and 14.7% across nine cultivars , respectively. Our results are similar to the relative concentration of glutamic acid observed in Fuji apples grown in China (7.7%) and some Spanish cider apples, for which the relative concentration of glutamic acid was 5.9% across 17 cultivars .…”