# Microalgal Proteins and Bioactives for Food, Feed, and Other Applications
## 1 Introduction
### Microalgae for Food and Functional Food Applications
#### 1.1.2 Lipids  
Microalgae are an excellent source of the polyunsaturated fatty acids (PUFAs) omega-3 and omega-6, as well as sterols [63]. Humans and mammals lack the delta-12 and delta-15 desaturase enzymes, which have the ability to convert oleic acid into linoleic and \(\alpha\)-linoleic acids. Because of this, it is essential to include PUFAs in sufficient amounts (males and females 0.25 g of EPA and DHA daily) in the human diet [64]. Microalgae species such as _Nammochloropsis gaditana_, _Nammochloropsis oculata_, _Pavlova lutheri_, _Phaodactylum tricontum_ and _Tetradesmus pseudonana_ are an excellent source of eicosapentaenoic acid (EPA), while others such as _Schizochytrium_ sp., _Isochryssi_ sp. and _Pavlova lutheri_ are rich in docosahexaenoic-aenoic acid (DHA). Arachidonic acid is found in _Parietochloris incisa_; gamma linoleic acid is found in _Arthospira_ sp. as well as stearidonic acid [8]. Enhanced PUFA levels can be \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Species** & \begin{tabular}{c} **Enzyme Used** \\ **for Hydrolysis** \\ \end{tabular} & **Petide** & **Effect** & **References** \\ \hline \multirow{3}{*}{_Chlorella_ _pyrenoidosis_} & Trypsin, & \begin{tabular}{c} \(\mathrm{FIKPLGSGK}\) \\ \(\mathrm{QYTMGK}\) \\ \(\mathrm{LFVAEAIYK}\) \\ \(\mathrm{QHAGTKAK}\) \\ \end{tabular} & ACE-inhibitory & \multirow{3}{*}{[53]} \\  & & \begin{tabular}{c} \(\mathrm{DPP-IV}\) \\ \(\mathrm{inhibitory}\) \\ \end{tabular} & [53] \\ \hline \multirow{3}{*}{_Chlorella_ _pyrenoidosis_} & \begin{tabular}{c} \(\mathrm{Pepsin}\), \\ \(\mathrm{flavourzyme}\), \\ \(\mathrm{alcalase}\), and \\ \(\mathrm{papain}\) \\ \end{tabular} & \begin{tabular}{c} \(\mathrm{VECYGPNRPQF}\) \\ \(\mathrm{antimap}\) \\ \(\mathrm{atherosclerotic}\) \\ \end{tabular} & \multirow{3}{*}{[54]} \\  & & \begin{tabular}{c} \(\mathrm{DPP-IV}\) \\ \(\mathrm{inhibitory}\) \\ \(\mathrm{ACE-1}\) inhibitory \\ \end{tabular} & & \\ \hline \multirow{3}{*}{_Chlorella vulgaris_} & \multirow{3}{*}{Pepsin} & \multirow{3}{*}{VECYGPNRPQF} & Protective effect & \multirow{3}{*}{[56]} \\  & & \begin{tabular}{c} on DNA \\ Antioxidant \\ \end{tabular} & & \\ \hline \multirow{3}{*}{_Chlorella vulgaris_} & \multirow{3}{*}{Pepsin} & IVVE & \multirow{3}{*}{ACE-1 inhibitory} & \multirow{3}{*}{[50]} \\  & & \begin{tabular}{c} AFL \\ \(\mathrm{AEL}\) \\ \(\mathrm{VVPPA}\) \\ \end{tabular} & & \\ \hline \multirow{3}{*}{_Disochrysis_ _zhanjiangensis_} & \multirow{3}{*}{Chymotrypsin} & \multirow{3}{*}{NDAEYGICGF} & \multirow{3}{*}{Antioxidant} & \multirow{3}{*}{[57]} \\  & & & & \\ \hline \multirow{3}{*}{_Nannochloropsis_ _oculata_} & \multirow{3}{*}{Alcalase} & LVTVM & ACE-inhibitory & [58] \\  & & & & \\ \hline \multirow{3}{*}{_Nannochloropsis_ _oculata_} & \multirow{3}{*}{Pepsin} & GMNNLTP & \multirow{3}{*}{ACE-inhibitory} & \multirow{3}{*}{[59]} \\  & & \begin{tabular}{c} LEQ \\ \end{tabular} & & \\ \hline \multirow{3}{*}{_Navicula incorta_} & \multirow{3}{*}{Papain} & n/d & \multirow{3}{*}{\begin{tabular}{c} Cytoprotective \\ effect \\ Antioxidant \\ \end{tabular} } & \\ \hline \multirow{3}{*}{_Navicula incorta_} & \multirow{3}{*}{Alcalase} & \multirow{3}{*}{n/d} & \multirow{3}{*}{n/d} & \multirow{3}{*}{Antioxidant} & \multirow{3}{*}{[61]} \\  & & \
\begin{tabular}{c} pronase-E, \\ \(\mathrm{\alpha}\)-chymotrypsin \\ \end{tabular} & & \\ \hline \multirow{3}{*}{_Tetradesmus_ _obliquus_} & \multirow{3}{*}{Alcalase} & WPRGYL & \multirow{3}{*}{Antioxidant} & \multirow{3}{*}{[62]} \\  & &
\begin{tabular}{c} GPDRPKFLGPF \\ WYGPDRPKFL \\ SDWDRF \\ \end{tabular} & & \\ \hline \hline \end{tabular} n/d = peptide sequences not characterised.  
\end{table} 
Table 3: _Cont._achieved by applying various types of abiotic stress to microalgae during cultivation. The methods used to increase PUFA levels in microalgae include nutrient depletion, commonly known as nitrogen starvation, or adjusting salinity, pH and temperature conditions [65; 66].