FTIR spectra of whey and casein hydrolysates in relation to their functional properties     

Van Der Ven C  Muresan S  Gruppen H  De Bont DB  Merck KB  Voragen AG 《Journal of agricultural and food chemistry》2002,50(24):6943-6950

Mid-infrared spectra of whey and casein hydrolysates were recorded using Fourier transform infrared (FTIR) spectroscopy. Multivariate data analysis techniques were used to investigate the capacity of FTIR spectra to classify hydrolysates and to study the ability of the spectra to predict bitterness, solubility, emulsifying, and foaming properties of hydrolysates. Principal component analysis revealed that hydrolysates prepared from different protein sources or with different classes of proteolytic enzymes are distinguished effectively on basis of their FTIR spectra. Moreover, multivariate regression analysis showed satisfactory to good prediction of functional parameters; the coefficient of determination (R(2)) varied from 0.60 to 0.92. The accurate prediction of bitterness and emulsion forming ability of hydrolysates by using only one uncomplicated and rapid analytical method has not been reported before. FTIR spectra in combination with multivariate data analysis proved to be valuable in protein hydrolysate fingerprinting and can be used as an alternative for laborious functionality measurements.  相似文献   

Flavor release and perception of flavored whey protein gels: perception is determined by texture rather than by release     

Weel KG  Boelrijk AE  Alting AC  Van Mil PJ  Burger JJ  Gruppen H  Voragen AG  Smit G 《Journal of agricultural and food chemistry》2002,50(18):5149-5155

Five whey protein gels, with different gel hardnesses and waterholding capacities, were flavored with ethylbutyrate or diacetyl and evaluated by a 10-person panel to study the relation between the gel structure and the sensory perception, as well as the nosespace flavor concentration during eating. The sensory perception of the flavor compounds was measured by the time-intensity method, while simultaneously the nosespace flavor concentration was monitored by the MS-Nose. The nosespace flavor concentration was found to be independent of the gel hardness or waterholding capacity. However, significant changes in flavor intensity between the gels were perceived by the majority of the panelists, despite the fact that the panelists were instructed to focus only on flavor perception and to not take texture into account. From these observations it is concluded that the texture of gels determines perception of flavor intensity rather than the in-nose flavor concentration.  相似文献   

Peroxidase-mediated cross-linking of a tyrosine-containing peptide with ferulic acid   总被引：4，自引：0，他引：4  

Oudgenoeg G  Hilhorst R  Piersma SR  Boeriu CG  Gruppen H  Hessing M  Voragen AG  Laane C 《Journal of agricultural and food chemistry》2001,49(5):2503-2510

The tyrosine-containing peptide Gly-Tyr-Gly (GYG) was oxidatively cross-linked by horseradish peroxidase in the presence of hydrogen peroxide. As products, covalently coupled di- to pentamers of the peptide were identified by LC-MS. Oxidative cross-linking of ferulic acid with horseradish peroxidase and hydrogen peroxide resulted in the formation of dehydrodimers. Kinetic studies of conversion rates of either the peptide or ferulic acid revealed conditions that allow formation of heteroadducts of GYG and ferulic acid. To a GYG-containing incubation mixture was added ferulic acid in small aliquots, therewith keeping the molar ratio of the substrates favorable for hetero-cross-linking. This resulted in a predominant product consisting of two ferulic acid molecules dehydrogenatively linked to a single peptide and, furthermore, two ferulic acids linked to peptide oligomers, ranging from dimers to pentamers. Also, mono- and dimers of the peptide were linked to one molecule of ferulic acid. A mechanism explaining the formation of all these products is proposed.  相似文献   

Formation and stability of foams made with sunflower (Helianthus annuus) proteins     

González-Pérez S  Vereijken JM  van Koningsveld GA  Gruppen H  Voragen AG 《Journal of agricultural and food chemistry》2005,53(16):6469-6476

Foam properties of a sunflower isolate (SI), as well as those of helianthinin and sunflower albumins (SFAs), were studied at various pH values and ionic strengths and after heat treatment. Less foam could be formed from helianthinin than from SFAs, but foam prepared with helianthinin was more stable against Ostwald ripening and drainage than foam prepared with SFAs. Foams made with SFAs suffered from extensive coalescence. The formation and stability of foams made from reconstituted mixtures of both proteins and from SI showed the deteriorating effect of SFAs on foam stability. Foam stability against Ostwald ripening increased after acid and heat treatment of helianthinin. Partial unfolding of sunflower proteins, resulting in increased structural flexibility, improved protein performance at the air/water interface. Furthermore, it was observed that the protein available is used inefficiently and that typically only approximately 20% of the protein present is incorporated in the foam.  相似文献   

Structure and stability of the potato cysteine protease inhibitor group (cv. Elkana)     

Pouvreau L  Kroef T  Gruppen H  van Koningsveld G  van den Broek LA  Voragen AG 《Journal of agricultural and food chemistry》2005,53(14):5739-5746

The conformational stability of potato cysteine protease inhibitor (PCPI), the second most abundant protease inhibitor group in potato tuber, was investigated at ambient temperature and upon heating using far- and near-UV circular dichroism spectroscopy, fluorescence spectroscopy, and differential scanning calorimetry (DSC). The PCPI isoforms investigated have a highly similar structure at both the secondary and the tertiary level. PCPI isoforms show structural properties similar to those of the potato serine protease inhibitor group and the Kunitz type soybean trypsin inhibitor, a known beta-II protein. Therefore, PCPI isoforms are also classified as members of the beta-II protein subclass. Results show that the thermal unfolding of PCPI isoforms does not follow a two-state mechanism and that at least one intermediate is present. The occurrence of this intermediate is most apparent in the thermal unfolding of PCPI 8.3 as indicated by the presence of two peaks in the DSC thermogram. Additionally, the formation of aggregates (>100 kDa), especially at low scan rates, increases the apparent cooperativity of the unfolding.  相似文献   

Relative abundance and inhibitory distribution of protease inhibitors in potato juice from cv. Elkana.     

L Pouvreau  H Gruppen  S R Piersma  L A van den Broek  G A van Koningsveld  A G Voragen 《Journal of agricultural and food chemistry》2001,49(6):2864-2874

Protease inhibitors from potato juice of cv. Elkana were purified and quantified. The protease inhibitors represent ca. 50% of the total soluble proteins in potato juice. The protease inhibitors were classified into seven different families: potato inhibitor I (PI-1), potato inhibitor II (PI-2), potato cysteine protease inhibitor (PCPI), potato aspartate protease inhibitor (PAPI), potato Kunitz-type protease inhibitor (PKPI), potato carboxypeptidase inhibitor (PCI), and "other serine protease inhibitors". The most abundant families were the PI-2 and PCPI families, representing 22 and 12% of all proteins in potato juice, respectively. Potato protease inhibitors show a broad spectrum of enzyme inhibition. All the families (except PCI) inhibited trypsin and/or chymotrypsin. PI-2 isoforms exhibit 82 and 50% of the total trypsin and chymotrypsin inhibiting activity, respectively. A strong variation within the latter activities was shown within one family and between protease inhibitor families.  相似文献   

Conformational stability of the potato serine protease inhibitor group     

Pouvreau L  Gruppen H  van Koningsveld G  van den Broek LA  Voragen AG 《Journal of agricultural and food chemistry》2005,53(8):3191-3196

The thermal unfolding of potato serine protease inhibitor (PSPI), the most abundant protease inhibitor group in potato tuber, was measured using far UV CD spectroscopy, fluorescence spectroscopy, and DSC. The results indicate that the thermal as well as the guanidinium-induced unfolding of PSPI occurs via a non-two-state mechanism in which at least one stable intermediate is present. Additionally, the occurrence of aggregation, especially at low scan rates, increases the apparent cooperativity of the unfolding and makes the system kinetically rather than thermodynamically controlled. Aggregate formation seems to occur via a specific mechanism of which PSPI in a tetrameric form is the end product and which may involve disulfide interchanges.  相似文献   

Effect of emulsion properties on release of esters under static headspace, in vivo, and artificial throat conditions in relation to sensory intensity     

Weel KG  Boelrijk AE  Burger JJ  Jacobs MA  Gruppen H  Voragen AG  Smit G 《Journal of agricultural and food chemistry》2004,52(21):6572-6577

The effects of oil content and droplet size distributions of dilute oil-in-water emulsions on release of four esters with different hydrophobicities were studied under in vivo, static headspace, and artificial throat conditions. The effect of oil content on orthonasal and retronasal perceived intensity of ethyl hexanoate was studied using a seven-person panel. With increasing oil content and with a higher hydrophobicity of the aroma compound, a stronger decrease in aroma release was found. This effect was stronger under static headspace conditions than under in vivo and artificial throat conditions, and the sensory intensity of ethyl hexanoate was perceived stronger orthonasally than retronasally. The lowest effective oil content was determined for all systems. Of the compounds tested, droplet size distribution only influenced the in vivo release of geranyl acetate. The artificial throat results correlated well with in vivo release, giving support to the assumption that a thin layer of liquid remaining in the throat after swallowing determines aroma release.  相似文献   

Partially Molten Middle Crust Beneath Southern Tibet: Synthesis of Project INDEPTH Results   总被引：23，自引：0，他引：23  

KD Nelson  W Zhao  LD Brown  J Kuo  J Che  X Liu  SL Klemperer  Y Makovsky  R Meissner  J Mechie  R Kind  F Wenzel  J Ni  J Nabelek  C Leshou  H Tan  W Wei  AG Jones  J Booker  M Unsworth  WSF Kidd  M Hauck  D Alsdorf  A Ross  M Cogan  C Wu  E Sandvol  M Edwards 《Science (New York, N.Y.)》1996,274(5293):1684-1688

INDEPTH geophysical and geological observations imply that a partially molten midcrustal layer exists beneath southern Tibet. This partially molten layer has been produced by crustal thickening and behaves as a fluid on the time scale of Himalayan deformation. It is confined on the south by the structurally imbricated Indian crust underlying the Tethyan and High Himalaya and is underlain, apparently, by a stiff Indian mantle lid. The results suggest that during Neogene time the underthrusting Indian crust has acted as a plunger, displacing the molten middle crust to the north while at the same time contributing to this layer by melting and ductile flow. Viewed broadly, the Neogene evolution of the Himalaya is essentially a record of the southward extrusion of the partially molten middle crust underlying southern Tibet.  相似文献   

Crystalline Ropes of Metallic Carbon Nanotubes   总被引：7，自引：0，他引：7  

A Thess  R Lee  P Nikolaev  H Dai  P Petit  J Robert  C Xu  YH Lee  SG Kim  AG Rinzler  DT Colbert  GE Scuseria  D Tomanek  JE Fischer  RE Smalley 《Science (New York, N.Y.)》1996,273(5274):483-487

Fullerene single-wall nanotubes (SWNTs) were produced in yields of more than 70 percent by condensation of a laser-vaporized carbon-nickel-cobalt mixture at 1200degreesC. X-ray diffraction and electron microscopy showed that these SWNTs are nearly uniform in diameter and that they self-organize into "ropes," which consist of 100 to 500 SWNTs in a two-dimensional triangular lattice with a lattice constant of 17 angstroms. The x-ray form factor is consistent with that of uniformly charged cylinders 13.8 +/- 0.2 angstroms in diameter. The ropes were metallic, with a single-rope resistivity of <10(-4) ohm-centimeters at 300 kelvin. The uniformity of SWNT diameter is attributed to the efficient annealing of an initial fullerene tubelet kept open by a few metal atoms; the optimum diameter is determined by competition between the strain energy of curvature of the graphene sheet and the dangling-bond energy of the open edge, where growth occurs. These factors strongly favor the metallic (10,10) tube with C5v symmetry and an open edge stabilized by triple bonds.  相似文献