Microalgae are known to have higher photosynthetic efficiencies when compared to land-based plants. The use of microalgae biomass as a protein source is attracting attention due to its interesting protein composition and sustainable character when compared to conventional animal and plant protein-based sources. Nonetheless, the existence of a rigid cell wall is typical for most microalgae species, and this presents a serious obstacle to a higher bioaccessibility of their valuable protein fractions. Depending on the cell wall composition, the gastrointestinal digestion process itself can result in different pathways of protein absorption. It is then important to understand how microalgae cell wall structure can be affected during traditional and industrial production of its biomass once these questions are often overlooked. This review intends to fulfill this gap by addressing the major impacts of innovative sustainable processing of microalgae biomass, giving particular attention to drying operations and cellular disruption methods based on electric field application—such as pulsed electric fields (PEF) and moderate electric fields (MEF). Using microalgae biomass as food supplements at its full potential depends on its protein digestibility patterns, and subsequently their bioaccessibility and bioavailability. The importance of using in vitro gastrointestinal systems to understand the impact of innovative downstream processing of microalgae biomass will be addressed.

β-Lactoglobulin (β-LG) encompasses important biological functions, but it is also a major milk allergen, being responsible for the high incidence of cow's milk allergy in childhood. Despite numerous studies addressing the effect of thermal processing on the immunoreactivity of β-LG, little is known about the impact of emergent food processing technologies, such as ohmic heating (OH), on its immunoreactivity. This study describes, for the first time, the effects of thermal and electric effects of OH on the immunoreactivity of β-LG. The influence of high-temperature short time (HTST; 72.5 °C for 15 and 90 °C for 1 s) and low-temperature long time (LTLT; 65 °C for 30 min) pasteurization binomials combined with different electrical variables (electric field intensity and electrical frequency) was evaluated and compared with that of conventional heating. HTST at 90 °C for 1 s extensively affects the protein secondary structure and increases the levels of reactive aggregates, resulting in increased total immunoreactivity (assessed by ELISA and immunoblotting). OH at 4 V cm⁻¹ and a frequency of 25 kHz reduced the immunoreactivity of monomeric β-LG and its resultant aggregates, compared with conventional heat treatments. In contrast, the presence of electric fields (4 V cm⁻¹ and 25 kHz) during LTLT increased the immunoreactivity of monomeric β-LG. The thermal and electrical variables of OH change the balance between monomeric and aggregated forms of β-LG, affecting their ability to bind specific antibodies. These outcomes bring novel insights into how to modulate OH aiming at reducing the allergenic potential of β-LG based products.

A significant fraction of the food produced worldwide is currently lost or wasted throughout the supply chain, squandering natural and economic resources. Food waste valorization will be an important necessity in the coming years. This work investigates the ability of food waste to serve as a viable nutritional substrate for the heterotrophic growth of Chlorella vulgaris. The impact of different pretreatments on the elemental composition and microbial contamination of seven retail food waste mixtures was evaluated. Among the pretreatment methods applied to the food waste formulations, autoclaving was able to eliminate all microbial contamination and increase the availability of reducing sugars by 30%. Ohmic heating was also able to eliminate most of the contaminations in the food wastes in shorter time periods than autoclave. However, it has reduced the availability of reducing sugars, making it less preferable for microalgae heterotrophic cultivation. The direct utilization of food waste containing essential nutrients from fruits, vegetables, dairy and bakery products, and meat on the heterotrophic growth of microalgae allowed a biomass concentration of 2.2 × 10⁸ cells·mL⁻¹, being the culture able to consume more than 42% of the reducing sugars present in the substrate, thus demonstrating the economic and environmental potential of these wastes.

Solid-state fermentation (SSF) involves the growth of microorganisms on solid substrates, mimicking natural environments of many species. Due to sustainability concerns, transforming agro-industrial by-products into value-added products through SSF has been increasingly studied. Brewer’s spent grain (BSG), the main by-product of beer production, mostly consists of barley grain husks, making BSG a great support for microorganism cultivation. Although autoclaving remains the standard sterilization and pretreatment method of substrates, electric field technologies and their attendant ohmic heating (OH) have great potential as an alternative technology. In the present work, pretreatment of BSG by OH was explored in SSF with Aspergillus niger to produce commercially valuable enzymes. OH favored the solubilization of phenolic compounds, total protein, and reducing sugars significantly higher than autoclaving. SSF of treated BSG led to the production of lignocellulosic enzymes, with xylanases being the most active, reaching 540 U/g, a 1.5-fold increase in activity compared to autoclaved BSG. Protease activity was also improved 1.6-fold by OH, resulting in 49 U/g. Our findings suggest that OH treatment is an effective alternative to autoclaving and that its integration with SSF is a sustainable strategy to enhance by-product valorization through enzyme production with many industrial applications, according to circular economy guidelines.

Solid-state fermentation (SSF) involves the growth of microorganisms on solid substrates, mimicking natural environments of many species. Due to sustainability concerns, transforming agro-industrial by-products into value-added products through SSF has been increasingly studied. Brewer’s spent grain (BSG), the main by-product of beer production, mostly consists of barley grain husks, making BSG a great support for microorganism cultivation. Although autoclaving remains the standard sterilization and pretreatment method of substrates, electric field technologies and its attendant ohmic heating (OH) have great potential as an alternative technology. In the present work, pretreatment of BSG by OH was explored in SSF with Aspergillus niger to produce commercially valuable enzymes. OH favored the solubilization of phenolic compounds, total protein and reducing sugars, significantly higher than autoclaving. SSF of treated BSG led to the production of lignocellulosic enzymes, with xylanases being the most active, reaching 540 U/g, a 1.5-fold increase in activity compared to autoclaved BSG. Protease activity was also improved 1.6-fold by OH, resulting in 49 U/g. Our findings suggest that OH treatment is an effective alternative to autoclaving and that its integration with SSF is a sustainable strategy to enhance by-products valorization through enzymes production with many industrial applications, according to circular economy guidelines.

Microalgae are widely used as dietary supplements. Despite their recognized nutritional value, it remains unclear whether consumption of microalgal biomass provides sufficient nutrient bioaccessibility to meet human dietary needs. In this work, the microalga Chlorella vulgaris CCAP 211/11B was cultivated and subjected to Pulsed Electric Fields (PEF) pre-treatment (20 kV·cm⁻¹, 100 kJ·kg⁻¹). The effects of PEF pretreatment were evaluated by assessing protein bioaccessibility throughout the different gastrointestinal (GI) digestion phases, as well as the amino acid profile and cytotoxicity in Caco-2 cells. During the oral and gastric phases, no significant differences (p > 0.05) in protein release were observed between PEF-treated and untreated biomass. At the final intestinal stage, however, protein release was 21.7% in PEF-treated biomass compared with 14.7% in untreated samples, corresponding to a 47% increase in protein bioaccessibility due to PEF pretreatment. Intrinsic fluorescence spectroscopy did not clearly discriminate treatments due to the dominant signal from digestive enzymes. Beyond improving protein availability, PEF-treated C. vulgaris exhibited no cytotoxic effects, confirming the safety of this processing approach for food applications aimed at enhancing protein uptake. Simulated GI digestion of both untreated and PEF-treated samples resulted in comparable amino acid profiles, with tyrosine, methionine, leucine, and lysine detected at the highest relative levels. Overall, these findings demonstrate that PEF treatment represents a promising strategy to enhance protein bioaccessibility in Chlorella vulgaris, thereby strengthening its potential as a functional and sustainable food supplement.