How to get Black Garlic?
Black Garlic`s characteristics are formed during the heat treatment when as a result of non-enzymatic browning reactions (Maillard reaction, chemical oxidation of phenols, caramelizing) the sugars react with amino acids and organoleptic, chemical and physical changes of a raw material occur (Bae et al., 2014).
How Black Garlic gets its colour?
Garlic acquires a dark brown or blackish color that is formed by melanoidin while higher temperatures produce more intense coloration (Kim et al., 2012). Unpleasant and pungent taste that characterizes typical garlics is replaced with mellow, sweet as well as sour and syrupy taste (Bae et al., 2014). Sweet taste is due to the degradation of polysaccharides into mono- and oligosaccharides under the influence of higher temperature. Sour tinge is caused by the drop in pH (due to the formation of carboxylic acids) (Zhang et al., 2014). While describing this sweet and sour taste at the same time, it is also referred to flavor nuances similar to balsamic vinegar and tamarind (Kim et al., 2012).
During treatment, the good qualities of garlics grow
Black Garlic has slightly caramel aroma. Compared to usual garlic, black garlic is softer by texture and with sticky gelatinous consistency (Bae et al., 2014). Besides, it has no digestion irritating side effects (Zhang et al., 2014).
The amount of natural sugars which is directly related to the sweetness of black garlic, increases from 28% in fresh garlic to 47% in black garlic. Other components as proteins and lipids don`t show quantitative differences compared to fresh garlic, although the amount of some specific amino acids grows remarkably after processing (Wang et al., 2010).
From the four identified sugars in garlic – sucrose, α-glucose, β-glucose and fructose – changes occurred in all types of sugars during heat treatment. Their concentration increases steadily during processing (Liang et al., 2015).
From amino acids the concentration of alanine, valine, leucine, isoleucine, lysine, arginine, proline, asparagine, aspartic acid, tyrosine, and phenylalanine increases in the beginning of manufacturing process. The concentration of other amino acids – threonine, glutamine, glutamic acid and tryptophan – however decreases continuously from the beginning of the process (Liang et al., 2015).
A sulfur-containing amino acid compound S- allyl cysteine (SAC) is especially important and in black garlic its concentration is 5-6 times higher than in fresh garlic (Bae et al., 2014).
Garlic, which has been treated at low temperature contains more SAC than the garlic that has been treated at higher temperatures. The effectiveness of lower temperature is related to the SAC formation mechanism. SAC is formed as a result of the enzymatic hydrolysis of g-glutamyl-S-allyl cysteine. The enzyme, which is responsible for the reaction, is g-glutamyl transpeptidase (g-GTP, EC 22.214.171.124), the activity of which is influenced by treatment temperature. The optimal temperature of the enzyme is at 40°C (Bae et al., 2014).
It has been suggested in the literature that the concentration of SAC could be the quality indicator of black garlic as this compound maintains the stability over a wide pH and temperature range (Bae et al., 2014).
From organic acids the acetic acid, formic acid, succinic acid and 3-hydroxypropionic acid are formed (Liang et al., 2015).