Performance of an ultrafiltration membrane bioreactor (UF-MBR) as a processing strategy for the synthesis of galacto-oligosaccharides at high substrate concentrations

Advances in Low-Lactose/Lactose-Free Dairy Products and Their Production

With increasing health awareness worldwide, lactose intolerance has become a major concern of consumers, creating new market opportunities for low-lactose/lactose-free dairy foods. In recent years, through innovating processes and technologies, dairy manufacturers have significantly improved the variety, and functional and sensory qualities of low-lactose and lactose-free dairy products. Based on this, this paper first covers the pathology and epidemiology of lactose intolerance and market trends. Then, we focus on current advantages and disadvantages of different lactose hydrolysis technologies and improvements in these technologies to enhance nutritional value, and functional, sensory, and quality properties of lactose-free dairy products. We found that more and more cutting-edge technologies are being applied to the production of lactose-free dairy products, and that these technologies greatly improve the quality and production efficiency of lactose-free dairy products. Hopefully, our review can provide a theoretical basis for the marketing expansion and consumption guidance for low-lactose/lactose-free dairy products.

Ultrasound-assisted enzymatic synthesis of galacto-oligosaccharides using native whey with two commercial β-galactosidases: Aspergillus oryzae and Kluyveromyces var lactis

Native whey obtained during casein micelle microfiltration was used as a novel source to produce galacto-oligosaccharides (GOS). Since the presence of macromolecules and other interferers reduces biocatalyst performance, this work evaluated the effect of different ultrasound processing conditions on GOS synthesis using concentrated native whey. Ultrasonic intensities (UI) below 11 W/cm² tended to increase the activity in the enzyme from Aspergillus oryzae for several minutes but accelerated the inactivation in that from Kluyveromyces lactis. At 40 °C, 40 % w/w native whey, 70 % wave amplitude, and 0.6 s/s duty-cycle, a UI of 30 W/cm² was achieved, and the increased specific enzyme productivity was similar to the values obtained with pure lactose (∼0.136 g GOS/h/mg_E). This strategy allows for obtaining a product containing prebiotics with the healthy and functional properties of whey proteins, avoiding the required purification steps used in the production of food-grade lactose.

Cyclic Production of Galacto-Oligosaccharides through Ultrafiltration-Assisted Enzyme Recovery

Galacto-oligosaccharides (GOS) are prebiotics manufactured enzymatically from lactose as substrate. The growing GOS market facilitates the valorization of dairy by-products which represent cheap and abundant sources of lactose. Large-scale GOS production typically employs soluble enzymes in batch reactors that are commonly associated with low enzyme usability and, therefore, high operational expenditures. In this study, we investigate the possibility of recovering enzymes by ultrafiltration (UF) and reusing them in repeated reaction steps. The proposed process scheme included 24 h batch reaction steps with Biolacta N5, a commercial enzyme preparation of Bacillus circulans origin. The reaction steps were followed by UF steps to separate the carbohydrate products from the enzymes by applying a volume concentration factor of 8.6. Then, the collected biocatalysts were reused for repeated cycles by adding fresh lactose. Enzyme losses were quantified with a direct method by analyzing the underlying relationship between reaction rates and enzyme dosage obtained from additional experiments conducted with known enzyme loads. Within five cycles, the enzyme activity declined gradually from 923 to 8307 U·kg−1, and the half-life was estimated as ca. 15.3 h. The outcomes of this study may serve as a basis for further optimization of the reported process scheme with enhanced enzyme usability.

Recent Advances in the Application of Enzyme Processing Assisted by Ultrasound in Agri-Foods: A Review

The intensification of processes is essential for the sustainability of the biorefinery concept. Enzyme catalysis assisted by ultrasound (US) may offer interesting opportunities in the agri-food sector because the cavitation effect provided by this technology has been shown to improve the efficiency of the biocatalysts. This review presents the recent advances in this field, focused on three main applications: ultrasound-assisted enzymatic extractions (UAEE), US hydrolysis reactions, and synthesis reactions assisted by US for the manufacturing of agri-food produce and ingredients, enabling the upgrading of agro-industrial waste. Some theoretical and experimental aspects of US that must be considered are also reviewed. Ultrasonic intensity (UI) is the main parameter affecting the catalytic activity of enzymes, but a lack of standardization for its quantification makes it unsuitable to properly compare results. Applications of enzyme catalysis assisted by US in agri-foods have been mostly concentrated in UAEE of bioactive compounds. In second place, US hydrolysis reactions have been applied for juice and beverage manufacturing, with some interesting applications for producing bioactive peptides. In last place, a few efforts have been performed regarding synthesis reactions, mainly through trans and esterification to produce structured lipids and sugar esters, while incipient applications for the synthesis of oligosaccharides show promising results. In most cases, US has improved the reaction yield, but much information is lacking on how different sonication conditions affect kinetic parameters. Future research should be performed under a multidisciplinary approach for better comprehension of a very complex phenomenon that occurs in very short time periods.

Use of Membrane Technologies in Dairy Industry: An Overview

The use of treatments of segregated process streams as a water source, as well as technical fluid reuse as a source of value-added recovery products, is an emerging direction of resource recovery in several applications. Apart from the desired final product obtained in agro-food industries, one of the challenges is the recovery or separation of intermediate and/or secondary metabolites with high-added-value compounds (e.g., whey protein). In this way, processes based on membranes, such as microfiltration (MF), ultrafiltration (UF), nanofiltration (NF) and reverse osmosis (RO), could be integrated to treat these agro-industrial streams, such as milk and cheese whey. Therefore, the industrial application of membrane technologies in some processing stages could be a solution, replacing traditional processes or adding them into existing treatments. Therefore, greater efficiency, yield enhancement, energy or capital expenditure reduction or even an increase in sustainability by producing less waste, as well as by-product recovery and valorization opportunities, could be possible, in line with industrial symbiosis and circular economy principles. The maturity of membrane technologies in the dairy industry was analyzed for the possible integration options of membrane processes in their filtration treatment. The reported studies and developments showed a wide window of possible applications for membrane technologies in dairy industry treatments. Therefore, the integration of membrane processes into traditional processing schemes is presented in this work. Overall, it could be highlighted that membrane providers and agro-industries will continue with a gradual implementation of membrane technology integration in the production processes, referring to the progress reported on both the scientific literature and industrial solutions commercialized.

Continuous Production of Galacto-Oligosaccharides by an Enzyme Membrane Reactor Utilizing Free Enzymes

Galacto-oligosaccharides (GOS) are prebiotic compounds widely used for their health-promoting effects. Conventionally, GOS is produced by the enzymatic conversion of lactose in stirred tank reactors (STR). The high operational costs associated with enzyme inactivation and removal might be reduced by the application of enzyme membrane reactors (EMR). In this study, we aimed to assess the potential of continuous GOS production by EMR using soluble Biolacta N5, a Bacillus circulans-derived commercial enzyme preparation. The steady-state performance of the EMR equipped with an ultrafiltration module was investigated as function of residence time (1.1-2.8 h) and enzyme load (17-190 U·g-1) under fixed operational settings of temperature (50 °C), pH (6.0), lactose feed concentration (300 g·kg-1), and recirculation flow-rate (0.18 m3·h-1). Results indicate that the yield of oligosaccharides with higher degree of polymerization (DP3-6) in STR (approx. 38% on total carbohydrate basis) exceeds that measured in EMR (ranging from 24% to 33%). However, a stable catalytic performance without a significant deterioration in product quality was observed when operating the EMR for an extended period of time (> 120 h). Approx. 1.4 kg of DP3-6 was produced per one gram of crude enzyme preparation over the long-term campaigns, indicating that EMR efficiently recovers enzyme activity.

Recent advances and perspectives of ultrasound assisted membrane food processing

Power ultrasound (US) transmits substantial amounts of small mechanical movements serving for particle detaching in membrane filtrations. This topic has been reviewed in recent years mainly focused on the mechanisms by which the flux is improved under specific processing conditions. US also been shown to improve food quality by changing physical properties and modifying the activity of enzymes and microorganisms. Surprisingly, limited information exists regarding on how the application of US results in terms of process and quality during membrane filtration of complex matrices such as liquid foods. This review highlights the recent advances in the use of US in membrane filtration processes focused in the manufacturing of foodstuffs and food ingredients, and perspectives of novel hybrid membrane-US systems that may be quite interesting for this field. The application of US in food membrane processing increases the flux, but the lack of standardization regarding to experimental conditions, make suitable comparisons impossible. In this sense, careful attention must be paid regarding to the ultrasonic intensity (UI), the membrane configuration and type of transducers and volume of the treated solution. Dairy products are the most studied application of US membrane food processing, but research has been mainly focused on flux enhancement; hitherto there have been no reports of how operational variables in these processes affect critical aspects such as quality and food safety. Also, studies performed at industrial scale and economical assessments are still missing. Application of US combined with membrane operations such as reverse osmosis (RO), forward osmosis (FO) and enzyme membrane bioreactors (EMBR) may result interesting for the production of value-added foods. In the perspective of the authors, the stagnation of the development of acoustic filtration systems in food is due more to a prejudice on this subject, rather than actual impedance due to the lack of technological development of transducers. This later has shown important advances in the last years making them suitable for tailor made applications, thus opening several research opportunities to the food engineering not yet explored.

Synthesis and purification of galacto-oligosaccharides: state of the art

Lactose-derived non-digestible oligosaccharides are prominent components of functional foods. Among them, galacto-oligosaccharides (GOS) outstand for being prebiotics whose health-promoting effects are supported on strong scientific evidences, having unique properties as substitutes of human milk oligosaccharides in formulas for newborns and infants. GOS are currently produced enzymatically in a kinetically-controlled reaction of lactose transgalactosylation catalyzed by β-galactosidases from different microbial strains. The enzymatic synthesis of GOS, although being an established technology, still offers many technological challenges and opportunities for further development that has to be considered within the framework of functional foods which is the most rapidly expanding market within the food sector. This paper presents the current technological status of GOS production, its main achievements and challenges. Most of the problems yet to be solved refer to the rather low GOS yields attainable that rarely exceed 40 %, corresponding to lactose conversions around 60 %. This means that the product or reaction (raw GOS) contains significant amounts of residual lactose and monosaccharides (glucose and galactose). Efforts to increase such yields have been for the most part unsuccessful, even though improvements by genetic and protein engineering strategies are to be expected in the near future. Low yields impose a burden on downstream processing to obtain a GOS product of the required purity. Different strategies for raw GOS purification are reviewed and their technological significance is appraised.