Entsymaattinen ristisilloitus maitoproteiinigeelien rakenteenmuokkauksessa

Proteins are the structural building blocks of fermented dairy products such as yoghurt. The nature of the protein-protein interactions and the structure of the macromolecular matrices they form determine the textural and water holding properties of a gel. In this study, the potential of enzymatic cross-linking in modification of acid-induced milk protein gel structures was studied by using the oxidative enzymes laccase and tyrosinase as well as the acyltransferase transglutaminase. The efficiency of the cross-linking enzymes with dissimilar reaction mechanisms in modification of milk proteins at various colloidal (milk or caseinate) or molecular (native, unfolded) states was investigated. Effects of enzymatically formed inter-molecular covalent bonds on the gel formation dynamics and the textural and water holding properties of acid-induced milk protein gels were elucidated. The results presented in this study have shown that enzymatic cross-linking, even with the oxidative enzymes tyrosinase and laccase, alters the mechanical properties of acid-induced milk protein gels. However, the knowledge on the mode of action of these enzymes on proteins should be further elucidated in order to be able to exploit them as structure-engineering tools with maximum efficiency. Comparison of the action of tyrosinase and transglutaminase in milk showed that even rather similar extent of inter-molecular covalent linkages did not necessarily result in similar mechanical properties in final acid-induced gels. It was concluded that it is not solely the introduced covalent links but also the preceding impacts on colloidal interactions by physical means which determine the actual effect of cross-linking on the final product attributes. In this thesis, the potential of one oxidative enzyme, T. reesei tyrosinase (TrT), was demonstrated for the creation of intra-micellarly linked casein particles, similarly to TG. In the future, it will be necessary to determine the physicochemical properties of TrT-induced casein particles as compared to the TG-induced casein particles. Furthermore, in raw milk, TrT was the only enzyme able to increase the gel firmness. This makes TrT a potential enzyme for use in raw milk-based products such as cheese. Finally, elucidation of altered aggregation dynamics for cross-linked protein particles will help to determine the optimum production parameters in order to tailor protein gels for improved product characteristics.Hapanmaitotuotteissa kuten jogurtissa proteiinit muodostavat verkostorakenteen, jossa proteiinien väliset vuorovaikutukset ovat tärkeimpiä aistittavaan rakenteeseen ja vedensidontaominaisuuksiin vaikuttavia tekijöitä. Väitöskirjatutkimuksessa selvitettiin proteiinin entsymaattisen ristisilloituksen soveltuvuutta hapanmaitogeelien rakenteenmuokkaukseen. Tutkimuksessa käytettiin kahta hapettavaa entsyymiä, lakkaasia ja tyrosinaasia, sekä transglutaminaasia. Mekanismiltaan toisistaan eroavien entsyymien vaikutusta proteiinien ristisilloittamiseen tutkittiin maidossa sellaisenaan ja kolloidisessa kaseinaattiliuoksessa mutta myös molekyylitasolla toisistaan eroavissa natiivissa ja denaturoidussa laskorakenteissa. Lisäksi selvitettiin entsyymien katalysoimien kovalenttisten sidosten vaikutusta kemiallisesti hapatettujen maitogeelien rakenteenmuodostukseen sekä vedensidontaan. Tutkimuksen tulokset osoittavat, että entsymaattisella ristisilloituksella voidaan muokata hapatettujen maitogeelien mekaanisia ominaisuuksia, näin myös lakkaasilla ja tyrosinaasilla, jotka ovat uusia entsyymejä maitoproteiinien muokkauksessa. On tärkeää ymmärtää, miten käytetystä entsyymistä riippuvat molekyylitason erot kohdeproteiineissa vaikuttavat muodostuviin rakenteisiin. Tyrosinaasin ja transglutaminaasin (TG) vertailu maidonproteiinimatriisissa osoitti, että huolimatta muodostuneiden molekyylienvälisten sidosten samanlaisesta määrästä ristisilloitettujen geelien mekaaniset ominaisuudet saattoivat erota toisistaan merkittävästi. Näin voitiin päätellä, että mekaaniset ominaisuudet eivät riipu ainoastaan kovalenttisten sidosten määrästä, vaan myös niiden seurauksena muuttuvista kolloidisista vuorovaikutuksista. Väitöstutkimuksessa osoitettiin, että T. reesei-homeesta eristetty hapettava tyrosinaasi- entsyymi (TrT) muodostaa TG-entsyymin tapaan kaseiinimisellin sisäisiä sidoksia, joiden avulla kaseiinimiselli voidaan stabiloida partikkeliksi. Tulevaisuudessa tulisi selvittää kuinka TrT- ja TG-entsyymillä tuotetut kaseiinipartikkelit eroavat fysikaalis-kemiallisilta ominaisuuksiltaan. Väitöstutkimuksessa havaittiin myös, että TrT oli ainoa entsyymi, jolla raakamaidosta tehdyn hapatetun geelin kiinteyttä saatiin lisättyä. TrT-entsyymiä voitaisiin siten hyödyntää raakamaitopohjaisissa meijerituotteissa, kuten juustoissa. Ristisitovia entsyymejä hyödyntämällä voidaan muokata maitoproteiinien vuorovaikutuksia hapatuksen aikana ja saada siten aikaan rakenteeltaan uudentyyppisiä maitoproteiinigeelejä

Ovalbumin production using Trichoderma reesei culture and low-carbon energy could mitigate the environmental impacts of chicken-egg-derived ovalbumin

Ovalbumin (OVA) produced using the fungus Trichoderma reesei (Tr-OVA) could become a sustainable replacement for chicken egg white protein powder—a widely used ingredient in the food industry. Although the approach can generate OVA at pilot scale, the environmental impacts of industrial-scale production have not been explored. Here, we conducted an anticipatory life cycle assessment using data from a pilot study to compare the impacts of Tr-OVA production with an equivalent functional unit of dried chicken egg white protein produced in Finland, Germany and Poland. Tr-OVA production reduced most agriculture-associated impacts, such as global warming and land use. Increased impacts were mostly related to industrial inputs, such as electricity production, but were also associated with glucose consumption. Switching to low-carbon energy sources could further reduce environmental impact, demonstrating the potential benefits of cellular agriculture over livestock agriculture for OVA production.Peer reviewe

Impact of in vitro gastrointestinal digestion on peptide profile and bioactivity of cooked and non-cooked oat protein concentrates

Oat (Avena sativa) is one of the most cultivated and consumed cereals worldwide. Recognized among cereals for its high protein content (12% to 24%), it makes it an excellent source of bioactive peptides, which could be modified during processes such as heating and gastrointestinal digestion (GID). This work aims to evaluate the impact of heat treatment on the proteolysis of oat proteins and on the evolution of antioxidant peptide release during in vitro static GID, in terms of comparative analysis between cooked oat protein concentrate (COPC) and non-heated oat protein concentrate (OPC) samples. The protein extraction method and cooking procedure used showed no detrimental effects on protein quality. After GID, the proportion of free amino acids/dipeptides (40% for both samples (OPC and COPC), thus producing peptides with low molecular weight and enhanced bioactivity. Furthermore, during GID, the amino acid profile showed an increase in essential, positively-charged, hydrophobic and aromatic amino acids. At the end of GID, the reducing power of OPC and COPC increased >0.3 and 8-fold, respectively, in comparison to the non-digested samples; while ABTS•+ and DPPH• showed a >20-fold increase. Fe2+ chelating capacity of OPC and COPC was enhanced >4 times; similarly, Cu2+ chelation showed a >19-fold enhancement for OPC and >10 for COPC. β-carotene bleaching activity was improved 0.8 times in OPC and >9 times in COPC; the oxygen radical antioxidant capacity assay increased 2 times in OPC and >4.7 times in COPC, respectively. This study suggests that OPC after cooking and GID positively influenced the nutritional and bioactive properties of oat peptides. Thus, COPC could be used as a functional food ingredient with health-promoting effects, as hydrothermal treatment is frequently used for this type of cereals

Limited hydrolysis of rice endosperm protein for improved techno-functional properties

Limited hydrolysis of rice endosperm protein isolate was carried out with acid and neutral endoproteases to evaluate the relationship between degree of hydrolysis and techno-functional properties. The highest studied degree of hydrolysis was 5.4% corresponding to 55.2% protein solubility. Solubility increased as a function of degree of hydrolysis with higher efficiency by acid endoprotease. Colloidal stability of the protein suspensions steadily increased with increasing degree of hydrolysis. Higher colloidal stability values were achieved by neutral endoprotease (31–89%) compared to that by acid endoprotease (20–75%). On the other hand, the absolute values of zeta potential and surface hydrophobicity decreased as a function of degree of hydrolysis leading to higher values by neutral endoprotease (−21.4 mV and 21.7 mV) than by acid endoprotease (−813.4 mV and 11.7 mV). Foaming, gel formation and water holding properties improved only until degree of hydrolysis values of 1.5% (neural endoprotease) and 1.9% (acid endoprotease).</p