Article from MDPI
Legume-based drinks are an excellent alternative to cow’s milk, which has been swooping in consumer satisfaction rankings for years. Plant-based drinks are healthy foods, with a rich and balanced content and excellent protein intake, appreciated by those who do not choose food only based on taste.
However, the processing and storage of these foods poses a number of problems that technology has yet to convincingly solve. Furthermore, the characteristic “beantaste” often unwelcome to consumers is a major obstacle for them to be accepted by large slices of the market.
Meanwhile, scholars continue to experiment with alternatives and pursue new solutions. All this, of course, also taking into account the needs for economic and ecologic sustainability.
Milk consumption: why does it keep decreasing?
Milk is an important staple food. However, in recent years, its consumption has been decreasing while in parallel the demand for non-dairy drinks has continued to grow. However, cereal and nut-based beverages have a protein content generally lower than 1.5% against 3.5% of milk: therefore, they cannot adequately replace its protein intake.
But what is behind this rejection of dairy products? There are several reasons for this decrease in popularity. Namely:
- Consumers may opt for milk alternatives because of health reasons (e.g., lactose intolerance, cow’s milk allergy, hypercholesterolemia, hormones and antibiotic residues);
- The increasing popularity of alternative lifestyle choice (e.g., vegetarian/vegan diet, animal welfare) determines the preference for non-animal products;
- The huge environmental impact of livestock farms (which causes about 14.5% of all human-induced emissions) leads to ecological concerns (extensive land use, water footprint, CO2 and methane emissions).
The use of native leguminous proteins can help reduce the environmental impact. Thanks to their ability to give rise to symbiotic associations with nitrogen-fixing bacteria in the roots of plants, these sources make the use of fertilizing agents in the soil almost completely superfluous.
More about legume beverages
Technically, legume-based beverages are colloidal suspensions of plant material dissolved and disintegrated in water. Their appearance and texture closely resemble that of cow’s milk but with a more balanced composition:
- Rich in proteins and minerals, legumes milk-alternatives have a low glycemic index.
- Legume proteins, whose essential amino acid composition is complementary to that of cereals, are naturally gluten-free. This makes them safe for gluten intolerant/allergic consumers.
- Moreover, the protein intake of legume-based drinks (approx. 3-4%) is similar to that of cow’s milk (i.e., 3.3-3.5%), unlike the alternatives to milk based on cereals and nuts, from values typically comprised between 0.1% and 1.0%
Despite their excellent nutritional profiles, most of these vegetable drinks must face a number of limitations, mainly related to processing and storage problems, on the one hand, and flavor issues, on the other.
- Although several technologies are available today, none of them can be said to be entirely satisfactory. For example, heat treatment, pH change, ionic strength or the presence of salts can change the structure of proteins and affect their solubility. Protein solubility is generally greater with alkaline and acidic pHs (pH <4.0 and pH> 5.0), while it decreases as the pH approaches the isoelectric point (4.5 for pea and chickpea proteins).
- Another barrier between legume-based beverages and consumers is the characteristic “bean” flavor. To improve the sensory profile of these drinks, cooking has proven able to eliminate the legume flavor.
Processing and preservation technologies for legume beverages
As we have said, the processing and storage of plant-based beverages require the use of specific technological procedures. Each of these have indisputable advantages but also have a number of limitations.
- Colloidal grinding reduces the size of the dispersed phase particles, causing microbial deterioration that requires further pasteurization to ensure safe consumption of the product.
- Heat treatments such as pasteurization can cause an increase in the viscosity of the drink (especially in the case of chickpeas and peas, with a high starch content), compromising its stability.
- Very high pressure homogenization can be a good alternative to heat treatment to reduce the size of colloidal particles while simultaneously destroying microorganisms.
- Heat inactivation is now considered the most promising technique for removing the “bean flavor” from legume drinks. However, high temperatures can cause excessive protein denaturation, clumping, lower protein solubility, and nutrient losses (e.g. vitamins and minerals). Therefore the technique must be carefully developed and applied with all the necessary precautions.
Technology can still do a lot to improve the quality of legume-based beverages, increasing their physical stability (eg colloidal grinding) and microbial shelf-life.
Processing and preservation of vegetable drinks: an experiment
Technology can still do a lot to improve the quality of legume-based beverages by increasing their physical stability (e.g., colloidal grinding) and microbial shelf life. This is demonstrated by a recent experiment involving 150 g of dried legumes, soaked twice in hot tap water (30–35 ֯ C) and once in cold tap water (15-20 C) for approx. 16 h
Chickpea (Cicer arietinum L.)
Layout of the production steps used for the different pulse beverages obtained from 10% (w/v) of dry seeds: (a) Procedure A for sprouts; Procedure B for seeds
After boiling the soaked seeds for 30 minutes with fresh tap water, the legumes were divided into two parts. Cooking water was added to one, and fresh tap water to the other. Finally, both were ground with food processor, sieved and bottled in sterilized containers (100 C, 10 min).
- During the cold storage, a separation by sedimentation took place, showing that the suspensions developed were not stable. The better control over heat treatments (maximum temperature and time) did not cause any gel formation in the drinks.
- Further analysis of the beverages confirmed the suitability of the process (pressure cooking and sieving) to maintain the expected protein content. Both pulse drinks made with cooking water had higher protein values than fresh water, thus confirming the solubilization of proteins in water during the cooking phase.
- In addition, the flavor and texture also benefited respectively from the addition of fresh water and cooking water.
Despite the wide range of solutions and technologies at the service of the vegetable alternatives to milk industry, we are still a long way from finding the right fit. For example, to remove the legume flavor from the drink, the heat treatment (cooking and pasteurization) gave excellent results. However, high temperatures can compromise the physical stability of the liquid. This problem can be overcome with the colloidal grinding technique, following the use of enzymes and the addition of natural flavors to improve the organoleptic profile of the product. Finally, to reduce the size of the particles, improve the stabilization of beverages and extend their microbial shelf life, high pressure homogenization has proven to be extraordinary.