**5. Recent advances in production of bioactive compounds**

Fermentation by probiotic bacteria is an approach used to the preservation of food for a long time. Fermented commodity contains bioactive compounds owing to the activity of probiotics in foodstuffs. The bioactive substances produced by probiotics in functional foods prompt beneficial outcomes for consumers [30]. In this regard, *Enterococcus sps, streptococcus sps, Bacillus sps* have the ability to synthesize amino acids, such as tryptophan and tyrosine, which are claimed to be advantageous to the function of the male and female reproductive system. Not only that, some probiotics are capable of yielding vitamin B groups. For instance*, Lactococcus lactis*, *Bifidobacterium sps.*, *Lactococcus fermentum* CECT 5716, *Lactobacillus reuteri* JCM1112 and could take part in the production of vitamin B2 (responsible for energy metabolism), B6 (responsible for amino acid metabolism), B9 (responsible for energy metabolism), and B12 (responsible for helping red blood cell formation and making DNA), respectively. For producing bioactive in protein-based foods (such as meat products, dairy products, soy milk, etc.), lactic acid bacteria are considered nontrivial. Besides, fungal fermentation of foods is employed to produce bioactive peptides in both plant and animal sources. In this regard, proteolyze activity of *Aspergillus oryzae* and *Aspergillus flavipes* in goat milk brought about the generation of peptides with antimicrobial/antioxidant nature [30]. Another conventional method used for the generation of bioactive peptides is the enzymatic hydrolysis of protein, by which one or more peptidases are added to a reactor containing deionized water and concentrated protein and controlling the temperature and pH throughout the process [31]. In addition to these conventional techniques, there are also innovative technologies, such as ultrasound-assisted and subcritical water extraction, which have been operated to produce bioactive peptides. Ultrasound-assisted extraction is a non-thermal and green technology that works based upon mechanical waves with frequencies of higher than 20 kHz, which traverses through a medium. Ultrasound waves give rise to strong forces at a microscopic scale in form of vibrations with large amplitudes in the medium, which then cause physical or chemical changes in foods [30]. This technique can be performed along with enzymatic hydrolysis in order to accelerate the process. Liang et al. [32] utilized low-frequency ultrasound with powers between 45 and 65 W/L on the enzymolysis of corn protein, which resulted in the production of short-chain peptides with a molecular weight of 200–1000 Da (11.84%) and 1000–3000 Da (21.29%) at optimal condition. In another study with a similar approach, Guerra-Almonacid et al. [33] used ultrasonic pre-treatment with a frequency of 80 kHz and an amplitude of 100% for 10 min prior to enzymatic hydrolysis of the plant protein. They reported that this procedure produced hydrolysates that possessed molecular weight ranging from 8 to 20 kDa. Subcritical water is liquid water at temperatures from 100 to 374°C under pressure less than 22 MPa (below the critical point of water). Once the dissociation constant (Kw) of subcritical water escalates as a function of temperature, subcritical water behaves as an acid or base catalyst [30]. Espinoza et al. [34] stated that the optimal condition regarding hydrolysis of whey protein isolate using subcritical water was at 300°C for 40 min, in which the free amino acids generation, especially lysin, was the highest.
