William L. Kerr

1H NMR studies of molecular mobility in wheat starch

Abstract Pulsed 1H NMR was used to determine moisture content and molecular mobility of wheat starch suspensions at water activity (aw) values between 0 and 0.93. Moisture determination by NMR agreed well with gravimetric determinations (R2=0.99). Transverse proton relaxation (T2) of the systems were identified using single pulse and CPMG experiments. T2 associated with starch molecules increased linearly from 7.1 to 10.1 μs as aw increased from 0 to 0.93, due to plasticizing effects of water. T2 associated with water molecules showed a linear increase up to aw of 0.69. Results indicated that 1H NMR could be employed to determine moisture content of starch suspension and to identify and quantify the molecular motion of starch chains and water molecules of starch suspensions at low moisture levels.

Total phenolics content and antioxidant capacities of microencapsulated blueberry anthocyanins during in vitro digestion

The goal of this research was to investigate the change in phenolics content and antioxidant capacity of microencapsulated anthocyanins (ACNs) digested in vitro. Blueberry ACN microcapsules were prepared from two wall materials (whey protein isolate and gum arabic) and ACN powder, previously extracted with three solvent systems (acetonic, ethanolic, methanolic); this was then spray-dried. The physicochemical properties and release characteristics of the microcapsules were evaluated. Rehydrated gum arabic microcapsules retained more total ACNs but less ferric reducing power than did whey protein microcapsules. Ethanolic extracts retained most of the total ACNs while methanolic extracts possessed the highest antioxidant capacity. During in vitro digestion, gum arabic microcapsules had high release rates of phenolics with high antioxidant activity during the gastric phase. Whey protein microcapsules had comparably lower release rates but high antioxidant activity throughout digestion.

Separation and characterization of phenolic compounds from dry-blanched peanut skins by liquid chromatography–electrospray ionization mass spectrometry

A large variety of phenolic compounds, including phenolic acids (hydroxybenzoic acids, hydroxycinnamic acids, and their esters), stilbenes (trans-resveratrol and trans-piceatannol), flavan-3-ols (e.g., (-)-epicatechin, (+)-catechin, and their polymers {the proanthocyanidins, PACs}), other flavonoids (e.g., isoflavones, flavanols, and flavones, etc.) and biflavonoids (e.g., morelloflavone), were identified in dry-blanched peanut skins (PS) by this study. High-performance liquid chromatography (HPLC) coupled with electrospray ionization mass spectrometry (ESI-MS(n)) was applied to separate and identify the phenolic constituents. Reversed-phase HPLC was employed to separate free phenolic compounds as well as PAC monomers, dimers, and trimers. PACs with a degree of polymerization (DP) of >4 were chromatographed via hydrophilic interaction liquid chromatography (HILIC). Tentative identification of the separated phenolics was based solely on molecular ions and MS(n) fragmentation patterns acquired by ESI-MS in the negative-ion mode. The connection sequence of PAC oligomers (DP <5) could be deduced mainly through characteristic quinone methide (QM) cleavage ions. When the DP reached 6, only a proportion of the flavan-3-ols could be ascertained in the PACs because of the extremely complicated fragmentation patterns involved. The identification of free phenolic acids, stilbenes, and flavonoids was achieved by authentic commercial standards and also by published literature data. Quantification was performed based on peak areas of the UV (free phenolic compounds) or fluorescence (PACs) signals from the HPLC chromatograms and calibration curves of commercial standards. Overall, PS contain significantly more PACs compared to free phenolic compounds.

Milling and particle size of cowpea flour and snack chip quality

Abstract Texture and color attributes were determined for snack chips made from cowpea flour. Chips were prepared from flour milled through 0.5, 1.0, and 2.0 mm screens; in addition, the ratio of cowpea flour to cornstarch was varied. Snapping force was slightly higher for chips made from fine flour. In general, the ratio of total energy to peak force ( E/PkF ) determined by the Kramer shear test increased with more finely milled flour, or addition of starch. Color values ( L *, a *, and b *) indicated that chips with greater cowpea protein/cornstarch ratios were darker and browner. Discriminant function analysis was used to relate instrumental measurements to consumer hedonic scores. Of particular importance was the ( E/PkF ) ratio from the Kramer shear test. Chips with lower E/PkF values had higher acceptability scores. In turn, the E/PkF values were related to the extractable starch content. The apparent starch content was dependent on either the amount of starch added, or by the milling conditions. In general, chips produced from finely milled flours had greater apparent starch content than those produced from coarsely milled flours.

Antioxidant and enzyme inhibitory activities of blueberry anthocyanins prepared using different solvents.

We compared the biological activities of anthocyanins prepared from whole blueberries or pomace and extracted with acetone, ethanol, and methanol. Crude Amberlite extracts (CAE) and rehydrated powders of freeze-dried anthocyanins were used. Ethanolic CAE yielded the highest total monomeric anthocyanin content [TMAC] (160 ppm), ferric reducing antioxidant power [FRAP] (3.4 mM Fe(2+)), total phenolics content [TPC] (382 ppm gallic acid equivalents [GAE]), and α-amylase inhibitory activity (36.8%). The rehydrated powder from acetonic extract gave the greatest FRAP (5.19) and TPC (422.7). α-Amylase (26.1%) and α-glucosidase (91.5%) inhibitory activities were also sustained. Methanolic CAE yielded values intermediate between ethanolic and acetonic extracts. Comparison of mass spectra between Amberlite extracts and rehydrated preparations revealed putative degradation and dimerization products in the rehydrated powders, which could account for loss in biological activities for rehydrated methanolic and ethanolic powders. Results of this study provide useful information in optimizing anthocyanin preparation methods for improved biological activity.

In vitro release properties of encapsulated blueberry (Vaccinium ashei) extracts.

We aimed to determine the effect of encapsulation on the release properties of blueberry extracts during simulated gastrointestinal digestion. An ethanolic pomace extract was microencapsulated with whey protein isolate via spray drying. The in vitro release of monomeric anthocyanins, phenolics and ferric reducing antioxidant activity of the microcapsules (W) were evaluated for the microcapsules and two non-encapsulated systems: ethanolic pomace extract (P) and freeze-dried juice (F). Concentrations of anthocyanin and phenolics were normalised prior to digestion. Results showed that antioxidant activity was in the order of: F>W>P. Regardless of encapsulation, more phenolics were released from W and P than F. Anthocyanin concentration decreased after intestinal digestion for W, but remained constant for P and F. MALDI-MS showed similar spectra for P and F but not for W. The spray-dried product has comparable release characteristics to freeze-dried juice, and may be investigated for food applications.

Rheological characterization of a model suspension during pipe flow using MRI

This work continues the development of the use of magnetic resonance imaging (MRI) techniques to characterize fluid/particulate mixtures during pipe flow. A primary application of this research is to aseptic processing of these mixtures by heat treatment. The heat treatment of flowing fluid/particulate systems is influenced by the fact that incorporating particles into a suspending fluid alters the velocity profile during pipe flow, and therefore the residence time distribution in a thermal system. MRI techniques were used to noninvasively determine velocity profiles of pure fluids and fluid/particulate mixtures. With this information and a suspension rheology analysis, the relationship between relative viscosity, shear rate, and particle loading was determined. The results were characterized by a parameter that reflects the physics of particle migration during flow and the constitutive model for the viscosity as a function of particle loading. The predicted particle concentration varied between 50 and 150% of the average particle concentration, from a low loading in the high shear region near the pipe wall to a high particle loading at the pipe center.

Total phenolics content, anthocyanins, and dietary fiber content of apple pomace powders produced by vacuum-belt drying

BACKGROUND Apple pomace is a waste material from apple juice processing, and contains significant amounts of dietary fiber and phytochemicals. Many of these compounds may be degraded post-pressing and during drying operations. Continuous vacuum-belt drying (VBD) was studied as a means of drying and maintaining quality of apple pomace. The color and chemical properties of samples dried by vacuum-belt drying at different temperatures were evaluated including total phenolics content (TPC), monomeric anthocyanins (TMA) and dietary fiber content (TDF). RESULTS VBD powders were pale golden yellow, and those dried at 80°C did not differ in L*, a* and b* values from freeze-dried powders. VBD pomace had 44.9 to 51.9 g gallic acid equivalents kg(-1) TPC, with greatest retention for pomace dried at 80 and 95°C. TPC for pomace dried at 80 or 95°C was not significantly different from that for freeze-dried pomace. TMA levels (74.0 mg C3G kg(-1), where C3G is cyanidine 3-O-glucoside equivalents) were highest in pomace vacuum dried at 80°C. TDF ranged from 442 to 495 g kg(-1) in vacuum-dried pomace and was not significantly different from TDF of freeze-dried poamce (480 g kg(-1)). CONCLUSION In all cases, TPC, TMA and TDF were higher in VBD pomace than in freeze-dried whole apple, while VBD pomace prepared at 80 or 95°C had fiber and phytochemical levels similar to freeze-dried powders.

Formulation of a dry green tea-apple product: study on antioxidant and color stability.

A dry apple product enriched with green tea (GT) extract was designed as a novel food to deliver relevant amounts of catechins. The target water activity (a(w)) range between 0.11 and 0.32 was chosen for the GT-fortified apple, since it corresponds to low water mobility and, consequently, maximum stability of dehydrated apples. The GT-fortified product and a control dehydrated apple product were stored in air, at 30 degrees C, and evaluated for color, antioxidant contents (monomeric flavan 3-ols, total procyanidins, ascorbic acid, chlorogenic acid and dihydrochalcones), ferric reducing/antioxidant power (FRAP), and 2,2-diphenyl-1-(2,4,6-trinitrophenyl)hydrazyl radical (DPPH) scavenging capacity. After 1 mo of storage at the lowest a(w) level (0.11), the GT-fortified product retained 80 and 100% of the initial contents of the monomeric flavan 3-ols and total procyanidins, respectively. With increasing a(w) level to 0.32, the stability of antioxidants slowly decreased. The addition of GT to the apple product increased the FRAP value and the DPPH scavenging capacity by 3.6-fold and 4.6-fold respectively, which remained almost unchanged during storage. The GT-fortified product was similar in color to commercially available dehydrated apples. Results highlighted some advantages of using dehydrated apples as a target for green tea fortification, which deserve further trials to investigate potential applications for fortification of other dehydrated fruits.

Apple pomace is a good matrix for phytochemical retention.

Phytochemical content and color changes in dried apple pomace and pulp (mixture of Red Delicious and Golden Delicious varieties) were studied during 9 months storage in the water activity (a(w)) range 0.11-0.75 at 30 °C. Water mobility was measured at various a(w) levels by (1)H NMR. During storage, antioxidant degradation (including flavonols, flavanols, dihydrochalcones, anthocyanins, and hydroxycinnamic acids) followed first-order kinetics, whereas color changes followed zero-order kinetics. These changes were accelerated by increasing a(w). Phytochemical and color were more stable in the pomace than in the pulp over the entire a(w) range, having 2-6 times smaller degradation rates. These results were related to the lower water mobility found in apple pomace as compared to the pulp. The overall results show that apple pomace can be exploited as a food ingredient with good phytochemical retention, and may help in the development of new matrices with maximum phytochemical retention.