• Heat-induced Maillard reaction of the tripeptide IPP and ribose: Structural characterization and implication on bioactivity

      Jiang, Zhanmei; Rai, Dilip K.; O'Connor, Paula M.; Brodkorb, Andre; National Natural Science Foundation of China; Innovative Research Team of Higher Education of Heilongjiang Province (Elsevier, 28/09/2012)
      Maillard reaction products (MRPs) were prepared from aqueous model mixtures containing 60 g L− 1 ribose and 30 g L− 1 of the bioactive tripeptide IPP (Ile-Pro-Pro), heated at 98 °C. MRP and associated reactions with changes in IPP were observed within one hour of heat-treatment. The pH of MRPs decreased significantly during the heat treatment of IPP–ribose mixtures from 9.0 to 7.6 after one hour. The amino group content, IPP and ribose concentration decreased significantly during heat treatment. The fluorescence intensity of the IPP–ribose MRPs reached the maximum within 2 h. Modification of the UV/vis spectra for IPP–ribose MRPs was mainly due to a condensation reaction of IPP with ribose. Compounds with molecular weight between 300 and 650 Da were dominant while compounds smaller than 250 Da were also produced during the reactions, as characterized by size exclusion chromatography. Mass spectrometry revealed that IPP was conjugated to ribose at the N-terminal (m/z of 458.3) upon heat-treatment. The presence of ribose also promoted peptide degradation to dehydrated IP (m/z of 211.1). IPP–ribose MRPs lost the known angiotensin-I-converting enzyme (ACE) inhibitory activity of IPP; however, strong antioxidant properties were detected.
    • Integrated phenotypic-genotypic approach to understand the influence of ultrasound on metabolic response of Lactobacillus sakei

      Ojha, K. Shikha; Burgess, Catherine; Duffy, Geraldine; Kerry, Joseph P.; Tiwari, Brijesh K; Teagasc Walsh Fellowship Programme (PLOS, 2018-01-25)
      The lethal effects of soundwaves on a range of microorganisms have been known for almost a century whereas, the use of ultrasound to promote or control their activity is much more recent. Moreover, the fundamental molecular mechanism influencing the behaviour of microorganisms subjected to ultrasonic waves is not well established. In this study, we investigated the influence of ultrasonic frequencies of 20, 45, 130 and 950 kHz on growth kinetics of Lactobacillus sakei. A significant increase in the growth rate of L. sakei was observed following ultrasound treatment at 20 kHz despite the treatment yielding a significant reduction of ca. 3 log cfu/mL in cells count. Scanning electron microscopy showed that ultrasound caused significant changes on the cell surface of L. sakei culture with the formation of pores “sonoporation”. Phenotypic microarrays showed that all ultrasound treated L. sakei after exposure to various carbon, nitrogen, phosphorus and sulphur sources had significant variations in nutrient utilisation. Integration of this phenotypic data with the genome of L. sakei revealed that various metabolic pathways were being influenced by the ultrasound treatments. Results presented in this study showed that the physiological response of L. sakei in response to US is frequency dependent and that it can influence metabolic pathways. Hence, ultrasound treatments can be employed to modulate microbial activity for specialised applications.
    • Structure and antioxidant activity of Maillard reaction products from α-lactalbumin and β-lactoglobulin with ribose in an aqueous model system

      Jiang, Zhanmei; Brodkorb, Andre; Innovative Research Team of Higher Education of Heilongjiang Province; Program for New Century Excellent Talents in Heilongjiang Province University (Elsevier, 11/02/2012)
      Maillard reaction products (MRPs) were prepared from aqueous model mixtures containing 3% (w/w) ribose and 3% (w/w) of the dairy proteins α-lactalbumin (α-LA) or β-lactoglobulin (β-LG), heated at 95 °C, for up to 5 h. The pH of MRPs decreased significantly during heat treatment of α-LA-Ribose and β-LG-Ribose mixtures from 8.4 to 5.3. The amino group content in MRPs, derived from the α-LA-Ribose and β-LG-Ribose model system, was decreased noticeably during the first hour and did not change thereafter. The loss of free ribose in MRPs was higher for β-LG-Ribose than for α-LA-Ribose. During the Maillard reaction, the concentration of native and non-native α-LA, or β-LG, decreased and the formation of aggregates was observed. Fluorescence intensity of the β-LG-Ribose MRPs reached maximum within 1 h, compared to 2 h for α-LA-Ribose MRPs. Meanwhile, modification of the UV/vis absorption spectra for α-LA and β-LG was mainly due to a condensation reaction with ribose. Dynamic light scattering showed a significant increase in the particle size of the MRPs. Size exclusion chromatography of MRPs revealed the production of both high and low molecular weight material. Electrophoresis of MRPs indicated polymerization of α-LA and β-LG monomers via inter-molecular disulfide bridge, but also via other covelant bonds. MRPs from α-LA-Ribose and β-LG-Ribose exhibited increased antioxidant activities, therefore theses MRPs may be used as natural antioxidants in food products.