Presence of Unabsorbed Free Amino Acids at the End of the Small Intestine Indicates the Potential for an Increase in Amino Acid Uptake in Humans and Pigs.

BACKGROUND: Unabsorbed free amino acids (AAs) at the end of the small intestine result in a potential preventable nutritional loss. OBJECTIVES: This study aimed to quantify free AAs in terminal ileal digesta of both humans and pigs to investigate its relevance for the nutritional value of food proteins. METHODS: Two studies with three diets were performed: a human study-ileal digesta from eight adult ileostomates were collected over 9 h after ingestion of a single meal unsupplemented or supplemented with 30 g zein or whey; pig study-12 cannulated pigs were fed for 7 d with a diet containing whey or zein or no-protein diet, and ileal digesta were collected on the last 2 d. Digesta were analyzed for total and 13 free AAs. True ileal digestibility (TID) of AAs was compared with and without free AAs. RESULTS: All terminal ileal digesta samples contained free AAs. The TID of AAs in whey was 97% ± 2.4% (mean ± SD) in human ileostomates and 97% ± 1.9% in growing pigs. If the analyzed free AAs would have been absorbed, TID of whey would increase by 0.4%-units in humans and 0.1%-units in pigs. The TID of AAs in zein was 70% ± 16.4% in humans and 77% ± 20.6% in pigs and would increase by 2.3%-units and 3.5%-units, respectively, if the analyzed free AAs would have been fully absorbed. The largest difference was observed for threonine from zein: if free threonine was absorbed, the TID would increase by 6.6%-units in both species (P < 0.05). CONCLUSIONS: Free AAs are present at the end of the small intestine and can potentially have a nutritionally relevant effect for poorly digestible protein sources, whereas the effect is negligible for highly digestible protein sources. This result provides insight into the room for improvement of a protein's nutritional value if all free AAs are to be absorbed. J Nutr 2023;xx:xx-xx. This trial was registered at clinicaltrials.gov as NCT04207372.

In vitro digestibility of dietary proteins and in vitro DIAAS analytical workflow based on the INFOGEST static protocol and its validation with in vivo data.

The FAO recommends the digestible indispensable amino acid score (DIAAS) to determine protein quality in foods, preferably tested in vivo. Here, the INFOGESTin vitrodigestion protocol was applied and supplemented with an analytical workflow allowing the assessment of protein digestibility and DIAAS calculation. The protocol was applied to selected samples WPI, zein, collagen, black beans, pigeon peas, All-Bran®, and peanuts. The total protein digestibility, digestibility of individual amino acids (AA), and DIAAS values were established and compared with in vivo data for the same substrates. Total protein digestibility (total Nitrogen, r = 0.7, P < 0.05; primary amines (OPA), r = 0.6, P < 0.02; total AA, r = 0.6, P < 0.02) and digestibility of individual AA (r = 0.6, P < 0.0001) were in good agreement, between in vitro and in vivo, with a mean difference of 1.2 %. In vitro DIAAS was highly correlated with DIAAS obtained from in vivo true ileal digestibility values (r = 0.96, R2 = 0.89, P < 0.0001) with a mean difference of 0.1 %.

Kiwifruit (Actinidia deliciosa), compared with cellulose and psyllium, influences the histology and mucus layer of the gastrointestinal tract in the growing pig.

Kiwifruit (KF) fiber, a mixture of soluble and insoluble fibers, elicits mucosal changes in the gastrointestinal tract (GIT). This study aimed to define the nature of these changes in mucosal features throughout the GIT of the growing pig in response to semi-synthetic iso-fiber diets containing cellulose (CEL, low GIT luminal functionality) as the sole fiber source (4.5%), or diets where half of the CEL was replaced by either PSY fiber (PSY husk, high GIT luminal functionality) or KF fiber (consumed as intact fruit). Entire male growing pigs (n = 24, 21 kg bodyweight) received the three diets (n = 8) for 42 d. GIT tissues, digesta, and feces were sampled. The partial replacement of CEL increased (P≤ 0.05) the ileal (KF 22% and PSY 33%) and colonic (PSY 86%) mucus layer thickness, whereas it decreased the rectal crypt depth (KF -26%), and small intestinal (duodenum to ileum) villus length (PSY -17%). The number of duodenal goblet cells was 77% higher (P≤ 0.05) for KF than CEL. Pigs fed the KF-containing diet had greater (P≤ 0.05) apparent ileal organic matter digestibility and apparent total tract organic matter digestibility compared with CEL, but the lowest amount of fermented organic matter in the large intestine. In conclusion, partial substitution of CEL with PSY or KF at a constant, practically-relevant dietary fiber intake, affected several measures of GIT functionality with effects being specific to the added fiber.

Fatty Acids from Different Fat Sources and Dietary Calcium Concentration Differentially Affect Fecal Soap Formation in Growing Pigs.

BACKGROUND: Calcium (Ca) can complex with free fatty acids in the gastrointestinal tract (GIT), leading to the formation of insoluble unabsorbable Ca-fatty acid soaps, contributing to the proposed effect of Ca on weight loss in humans. OBJECTIVES: We determined the effect of dietary Ca concentration and the individual long-chain fatty acids on Ca-fatty acid soap formation and fatty acid digestibility. METHODS: Nine-week-old crossbreed male pigs (n = 144; mean ± SD body weight: 21.7 ± 0.15 kg) were used as an animal model for digestion in the adult human. The animals received purified diets containing 4 Ca concentrations (0, 2, 4, and 6 g/kg diet) and 4 fat sources (tallow, palmolein oil, soybean oil, and olive oil) in a completely randomized design. Fatty acids, Ca, and Ca-fatty acid soaps were determined in feces (n = 9 per diet). RESULTS: Increasing dietary Ca led to a 4-fold increase (P ≤ 0.05) in excreted palmitic and stearic acid when diets contained tallow or palmolein oil as the major fat source. More than 80% of these excreted fatty acids were present as soaps. For the tallow-based diets, increasing dietary Ca led to a decrease in stearic acid digestibility from 91% to 66% (P ≤ 0.01) and in palmitic acid digestibility from 96% to 83% (P ≤ 0.01). For the olive oil- and soybean oil-based diets dietary Ca did not (P > 0.05) influence fatty acid excretion. CONCLUSIONS: Ca-fatty acid soap formation led to decreased fat absorption in the GIT of growing pigs, which supports the hypothesis that higher dietary Ca concentrations reduce fat absorption.

In vitro ileal and caecal fermentation of fibre substrates in the growing pig given a human-type diet.

This study characterised the in vitro ileal fermentability of different substrates in the growing pig, adopted as an animal model for the adult human, and compared in vitro ileal and caecal fermentation in the pig. Substrates (arabinogalactan (AG), cellulose, fructo-oligosaccharide (FOS), inulin, mucin, citrus pectin and resistant starch) were fermented in vitro (ileal 2 h and caecal 24 h) with an ileal or caecal inoculum prepared from ileal or caecal digesta collected from growing pigs (n 5) fed a human-type diet for 15 d. The organic matter (OM) fermentability and production of organic acids were determined. In general, there was considerable in vitro ileal fermentation of fibre, and the substrates differed (P < 0·001) for both in vitro ileal and caecal OM fermentability and for organic acid production. Pectin had the greatest in vitro ileal OM fermentability (26 %) followed by AG, FOS and resistant starch (15 % on average), and cellulose, inulin and mucin (3 % on average). The fermentation of FOS, inulin and mucin was greater for in vitro caecal fermentation compared with the ileal counterpart (P ≤ 0·05). In general, the organic acid production was higher for in vitro caecal fermentation (P ≤ 0·05). For instance, the in vitro ileal acetic acid production represented 4-46 % of in vitro caecal production. Energy from fibre fermentation of 0·6-11 kJ/g substrate fermented could be expected in the ileum of the pig. In conclusion, substrates are fermented in both the ileum and caecum. The degree of fermentation varies among substrates, especially for in vitro ileal fermentation.

Orally administered ovine serum immunoglobulins modulate dental plaque in cats.

The effects of orally administered ovine serum immunoglobulin on dental plaque and associated oral immunity in cats were investigated. The two treatment groups consisted of 1) cats that were fed unsupplemented kibble (control diet) and 2) cats that were fed the same kibble but coated with a freeze-dried ovine serum immunoglobulin preparation (ovine Ig) (test diet). The adult cats were randomly allocated to one of the two diets (n = 15) and received their respective kibble for a 28-day experimental period. When compared to the ovine Ig-supplemented kibble, cats consuming the unsupplemented kibble had significantly (p < 0.05) higher dental plaque scores. Cat IgA and IgG concentrations in the saliva and serum were significantly (p < 0.05) higher for cats fed the unsupplemented kibble when compared to cats receiving the ovine Ig supplement. Similarly, myeloperoxidase activity in the saliva was significantly (p < 0.05) higher for cats fed the unsupplemented kibble when compared to cats receiving the Ig-supplement. Orally administered ovine serum Ig positively influenced oral health and oral immunity in cats as evidenced by preventing an increase of dental plaque formation, salivary and serum IgA and IgG concentrations and salivary myeloperoxidase activity.

Determination of True Ileal Amino Acid Digestibility in the Growing Pig for Calculation of Digestible Indispensable Amino Acid Score (DIAAS).

Digestible indispensable amino acid score (DIAAS) has been recommended by the FAO for the evaluation of protein quality in human foods, but the application of DIAAS is currently limited because of a lack of published data on the true ileal amino acid (AA) digestibility of AAs in foods. The importance of DIAAS is highlighted. To calculate DIAAS, it is necessary to determine the true ileal AA digestibility of human foods using the growing pig as an animal model for the human based on previous FAO recommendations. A method is described in detail in Supplemental Methods to determine the true ileal AA digestibility of foods for humans using the pig as a model for the adult human. Adoption of the method will enable consistency in the development of databases on predicted true ileal AA digestibility in human foods for the calculation of DIAAS.

Dietary supplementation with ovine serum immunoglobulin modulates correlations between mucin, microbiota and immunity proteins in the growing rat.

The objective of this study was to evaluate the relationship among the number of bacteria, number of goblet cells, gut mucin gene expression, mucin protein and immunity protein levels of rats fed a diet containing freeze-dried ovine Ig (FD). Sprague Dawley male rats were used in a 21-days study and were fed a basal control diet (BD; no Ig) and a test diet containing freeze-dried ovine Ig (FD). Diets were isocaloric and contained the same amount of the first limiting amino acids, methionine plus cysteine. Pearson's correlation analysis was conducted on the data (stomach, ileum and colon) obtained from individual rats (n = 10) fed either casein-based diet (BD) or ovine serum Ig (FD) to evaluate the relationship between number of bacteria, number of goblet cells, gut mucin gene expression and gut mucin protein levels. Pearson's correlation analysis was then conducted with the data from the FD fed rats to evaluate the relationship among the above said variables. In the stomach content, a significant (p < .05) correlation was found between the Muc5Ac gene expression and mucosal mucin protein. In the ileum and colon, a significant (p < .05) correlation was observed among the mRNA levels of mucin (Muc2 and Muc4) genes. There was also evidence of a strong relationship (p < .05) between digesta mucin and mucosal mucin protein concentrations. A negative correlation of mucosal IgA protein concentration with total Lactobacillus (in ileum and colon) and total bacteria (in the ileum) was not evident with FD fed rats when compared to the results obtained using both BD and FD fed rats. In conclusion, this study suggests that feeding freeze-dried ovine Ig in growing rats results in a strong correlation between the number of bacteria, mucin and immunity proteins.

Iron bioavailability of a casein-based iron fortificant compared with that of ferrous sulfate in whole milk: a randomized trial with a crossover design in adult women.

BACKGROUND: A highly soluble iron-casein complex has been developed for food fortification purposes with the aim to provide high iron bioavailability. OBJECTIVE: We aimed to determine the iron bioavailability of the iron-casein complex relative to that of ferrous sulfate (control) when given with whole milk in healthy young women. METHODS: A randomized comparator-controlled trial with a crossover design was conducted using the erythrocyte incorporation dual stable isotope (57Fe, 58Fe) technique. Iron absorption from the iron-casein complex was compared with that from ferrous sulfate in 21 healthy women aged 20-38 y with normal iron status. RESULTS: Fractional iron absorption (geometric mean; -SD, +SD) from the iron-casein complex (3.4%; 1.4%, 5.4%) and from ferrous sulfate (3.9%; 1.7%, 6.1%) were not statistically different (P > 0.05). The relative bioavailability value of the iron-casein complex to ferrous sulfate was determined to be 0.87 (-1 SD, +1 SD: -0.90, +2.64). CONCLUSIONS: The iron-casein complex has iron bioavailability comparable to that of ferrous sulfate in healthy young women. This trial was registered at www.anzctr.org.au as ACTRN12615000690550.

Food matrix and co-presence of turmeric compounds influence bioavailability of curcumin in healthy humans.

The natural food-derived compound curcumin (from turmeric root) is known for its anti-inflammatory and anti-oxidant effects. However, due to its poor solubility when consumed in isolation, it is poorly bioavailable. In this crossover study we compared the bioavailability of curcumin from a meal containing either curcumin powder, turmeric powder or grated fresh turmeric root, all containing 400 mg of curcumin, along with mashed potatoes and cream. Healthy male participants consumed the meals following overnight fasting, and postprandial blood samples were taken to measure plasma curcuminoids (curcumin, dimethylcurcumin (DMC) and bisdimethylcurcumin (BDMC)). All plasma curcumin values refer to total curcumin (sum of free and conjugated curcumin). The meals were also analysed using confocal laser scanning microscopy to determine the location of curcuminoids. Both of the turmeric meals produced significantly higher amounts (p < 0.05) of plasma curcuminoids at 1-3 hours after the meal was consumed, as compared to the curcumin powder. Plasma curcumin Cmax was 4.9 ng ml-1 95% CI (confidence interval) [2.2, 7.5] for the fresh turmeric meal, 8.4 ng ml-1 95% CI [4.4, 12.48] for the turmeric powder meal and 0.19 ng ml-1 95% [-0.08, 0.47] for the curcumin powder meal. Plasma DMC and BDMC were significantly higher (p < 0.05) following the turmeric powder meal, compared with the fresh turmeric meal and the curcumin powder meal. Microscopy images showed that the curcuminoid particles were mostly confined within curcuminoid cells in the fresh turmeric meal. They were unconfined but in clusters in the turmeric powder meal, while the curcuminoid particles appeared smaller in the curcumin powder meal. Conclusion: curcumin bioavailability is enhanced when consumed as fresh or powdered turmeric, which could be due to the co-presence of other turmeric compounds and/or a turmeric matrix effect.

The Rate at Which Digested Protein Enters the Small Intestine Modulates the Rate of Amino Acid Digestibility throughout the Small Intestine of Growing Pigs.

Background: Actinidin, a cysteine protease in kiwifruit (KF), increases both the gastric digestion and gastric-emptying rate of beef muscle protein. Objective: This study aimed to determine the relation between the rate of digested nitrogen entering the small intestine (SI; a function of the extent of gastric digestion and gastric-emptying rate) and the disappearance of amino acids (AAs) in different parts of the SI at set times postfeeding. Methods: Male 9-wk-old pigs (n = 90; mean ± SD body weight: 28 ± 2.9 kg) were fed a diet containing 14% beef for 3 d. The beef-based diet was supplemented with green KF pulp (containing actinidin), gold KF pulp supplemented with actinidin, or gold KF pulp alone (no actinidin). The KF or actinidin amounts corresponded to the intake of 2 KFs/human meal. On day 3, pigs were killed at 0.5, 1, 3, 5, and 7 h postprandially. Stomach chyme was analyzed to determine the rate of digested nitrogen entering the SI. Apparent AA digestibility at set times was determined in the proximal, medial, and distal SI. Polynomial and correlation analyses were conducted. Results: The rate of digested nitrogen entering the SI was higher (P < 0.001) with actinidin (e.g., >44% at 5 h postprandially). Actinidin also increased the apparent AA digestibility at the proximal and medial SI (P ≤ 0.05) at set times (e.g., 42% and 15% greater for arginine, respectively), but not in general for the distal SI (P > 0.05). At the proximal SI, apparent AA digestibility was correlated more strongly with the digested nitrogen entering the SI (r = 0.73, P < 0.001; n = 57) than with gastric emptying (r = 0.64, P < 0.001) or gastric protein digestion (r = 0.57, P < 0.001). Similar trends were observed for the medial SI. Conclusion: The rate of digested nitrogen entering the SI is an accurate predictor of the rate of AA digestibility and the location of AA absorption in the pig SI.

Effect of food matrix microstructure on stomach emptying rate and apparent ileal fatty acid digestibility of almond lipids.

Almond lipids can be consumed in different forms such as nuts, oil-in-water emulsions or oil. The stomach emptying rate (SER) of almond lipids (0.2 g of fat per 2 mL of almond lipid suspension) as a function of the food matrix was studied using magnetic resonance spectroscopy based on the stomach emptying of a marker (AlCl3-6H2O) in the growing rat. Chyme and digesta samples were collected following serial gavaging (0.2 g of fat per 2 mL of almond lipid suspension) to study microstructural changes and determine the apparent ileal digestibility of almond fatty acids as a function of the native food matrix. The T(1/2) for the stomach emptying of crushed whole almonds and almond cream (194 ± 17 min and 185 ± 19 min, respectively) were not different (P > 0.05) from that of a gastric-stable Tween-oil emulsion (197 ± 19 min). The T(1/2) values for a sodium caseinate (NaCas)-oil emulsion (145 ± 11 min) and a gastric-unstable Span-oil emulsion (135 ± 7 min) were different (P < 0.05) from those for crushed whole almonds, almond cream and Tween-oil emulsion, while almond milk and oil emptied at an intermediate rate (157 ± 9 min and 172 ± 11 min, respectively). Extensively coalesced emulsions under gastric conditions (almond oil, almond cream and Span-oil) had lower (P < 0.05) overall apparent ileal fatty acid digestibility (85.8%, 75.8% and 74.3%, respectively) than crushed whole almonds, almond milk, NaCas-oil and Tween-oil emulsions (91.0%, 92.2%, 92.1% and 88.7%, respectively). The original food matrix and structural changes occurring within the gastrointestinal tract had an impact on SER and ileal fatty acid digestibility of the almond preparations.

Korean ginseng modulates the ileal microbiota and mucin gene expression in the growing rat.

The study was conducted to investigate whether oral administration of Korean ginseng powders can modulate gut microbiota as well as intestinal mucin production at the translational and transcriptional levels in the ileum of the growing rat. Thirty individually caged Sprague-Dawley male rats were allocated to three groups (n = 10) and fed for 21 days either a basal control diet or one of the two treatment diets each containing white or red Korean ginseng (WG or RG) powder. Bacterial DNA was extracted from ileal digesta and subjected to quantitative real-time PCR (qPCR) using primers for total bacteria, Lactobacillus, Bifidobacteria, Escherichia coli, Bacteroides, and Clostridium strains. The qPCR results showed that consumption of WG or RG powder significantly increased the number of total bacteria and Lactobacillus strains compared to the control group. Consumption of WG powder increased mRNA expression of the Muc2 gene in the small intestine compared to the control group. There was no effect of WG or RG on the small intestinal digesta mucin content. Correlation analysis showed that expression of the Muc2 gene was significantly associated with the number of total bacteria (r = 0.52, P < 0.05) and Lactobacillus strains (r = 0.53, P < 0.05), respectively. Furthermore, the number of Lactobacillus strains was significantly correlated with the number of total bacteria (r = 0.87, P < 0.05). Consumption of the WG powder modulated the intestinal ecosystem of the growing rat and intestinal mucin gene expression.

Dietary actinidin from kiwifruit (Actinidia deliciosa cv. Hayward) increases gastric digestion and the gastric emptying rate of several dietary proteins in growing rats.

Dietary actinidin influences the extent to which some dietary proteins are digested in the stomach, and it is hypothesized that the latter modulation will in turn affect their gastric emptying rate (GE). In this study, the effect of dietary actinidin on GE and gastric digestion of 6 dietary protein sources was determined in growing rats. Each dietary protein source [beef muscle, gelatin, gluten, soy protein isolate (SPI), whey protein isolate, and zein] was included in 2 semisynthetic diets as the sole nitrogen source. For each protein source, 1 of the 2 diets contained actinidin [76.5 U/g dry matter (DM)] in the form of ground freeze-dried green kiwifruit (Actinidia deliciosa cv. Hayward), whereas the other diet contained freeze-dried gold kiwifruit (Actinidia chinensis cv. Hort16A), which is devoid of actinidin (3.4 U/g DM). For both diets, dietary kiwifruit represented 20% of the diet on a DM basis. The real-time GE was determined in rats gavaged with a single dose of the diets using magnetic resonance spectroscopy over 150 min (n = 8 per diet). Gastric protein digestion was determined based on the free amino groups in the stomach chyme collected from rats fed the diets (n = 8 per diet) that were later killed. GE differed across the protein sources [e.g., the half gastric emptying time (T(½)) ranged from 157 min for gluten to 266 min for zein] (P < 0.05). Dietary actinidin increased the gastric digestion of beef muscle (0.6-fold), gluten (3.2-fold), and SPI (0.6-fold) and increased the GE of the diets containing beef muscle (43% T(½)) and zein (23% T(½); P < 0.05). There was an inverse correlation between gastric protein digestion and DM retained in the stomach (r = -0.67; P < 0.05). In conclusion, dietary actinidin increased gastric protein digestion and accelerated the GE for several dietary protein sources. GE may be influenced by gastric protein digestion, and dietary actinidin can be used to modulate GE and protein digestion in the stomach of some dietary protein sources but not others.

Effects of season and plantation on phenolic content of unfermented and fermented Sri Lankan tea.

The effects of season and plantation on the polyphenol content of Camellia sinensis (tea) leaves were determined. Aqueous and organic extracts of freeze-dried fresh (unfermented) and black (fully-fermented) tea leaves were prepared for a structured set of samples (fermented and unfermented teas from six high-, mid- and low-grown plantations; fermented and unfermented teas from two harvesting seasons from four highland plantations), collected from the main tea-growing regions in Sri Lanka. Total catechin content and amounts of individual catechins, flavonols and theaflavins were determined by HPLC. Mean values for the phenolic constituents were generally significantly higher (p<0.05) with solvent extraction. The mean values for total catechins, total flavonols and caffeine in the aqueous extracts from unfermented teas were 10.6%, 1.5% and 2.9%, respectively. For both unfermented and fermented tea leaves, a significant (p<0.05) interaction between plantation and season was observed for phenolic constituents. Ferric reducing antioxidant power was positively (p<0.05) correlated with (-)-epicatechin gallate and total phenolic contents.

Actinidin from kiwifruit (Actinidia deliciosa cv. Hayward) increases the digestion and rate of gastric emptying of meat proteins in the growing pig.

The present study aimed to investigate the effect of dietary actinidin on the kinetics of gastric digestion of beef muscle proteins and on the rate of stomach emptying in growing pigs. For this purpose, 120 pigs (mean body weight 28 (sd 2·9) kg) were fed beef muscle protein-based diets containing either actinidin (fresh green kiwifruit pulp or gold kiwifruit pulp supplemented with purified actinidin) or no actinidin (fresh gold kiwifruit pulp or green kiwifruit pulp with inactivated actinidin). Additionally, fifteen pigs were fed with a protein-free diet to determine the endogenous protein flow. Pigs were euthanised at exactly 0·5, 1, 3, 5 and 7 h postprandially (n 6 per time point for each kiwifruit diet and n 3 for protein-free diet). Stomach chyme was collected for measuring gastric retention, actinidin activity, individual beef muscle protein digestion based on SDS-PAGE and the degree of hydrolysis based on the appearance of free amino groups. The stomach emptying of DM and N was faster when actinidin was present in the diet (P< 0·05): the half gastric emptying time of DM was 137 v. 172 min ( ± 7·4 min pooled standard error) for the diets with and without actinidin, respectively. The presence of dietary actinidin in the stomach chyme increased the digestion of beef muscle protein (P< 0·05) and, more specifically, those proteins with a high molecular weight (>34 kDa; P< 0·05). In conclusion, dietary actinidin fed in the form of fresh green kiwifruit increased the rate of gastric emptying and the digestion of several beef muscle proteins.

DPPH radical scavenging activity of a mixture of fatty acids and peptide-containing compounds in a protein hydrolysate of Jatropha curcas seed cake.

Jatropha curcas, a tropical plant, has great potential commercial relevance as its seeds have high oil content. The seeds can be processed into high-quality biofuel producing seed cake as a byproduct. The seed cake, however, has not gotten much attention toward its potential usefulness. This work was aimed to determine the antioxidant activity of different fractions of a protein hydrolysate from J. curcas seed cake and to elucidate the molecular structures of the antioxidants. Seed cake was first processed into crude protein isolate and the protein was hydrolyzed by Neutrase. The hydrolysate obtained from 1 h of Neutrase hydrolysis showed the strongest antioxidant activity against DPPH radical (2,2-diphenyl-1-picrylhydrazyl). After a purification series of protein hydrolysate by liquid chromatography, chemicals acting as DPPH radical inhibitors were found to be a mixture of fatty acids, fatty acid derivatives, and a small amount of peptides characterized by mass spectrometry and nuclear magnetic resonance (NMR) spectroscopy.

Complex rheological properties of a water-soluble extract from the fronds of the black tree fern, Cyathea medullaris.

A water-soluble extract was obtained from the fronds of a New Zealand native black tree fern (Cyathea medullaris or Mamaku in Maori). The extract exhibited complex rheological behavior. Newtonian, shear-thinning, shear-thickening, thixotropic, antithixotropic, and viscoelastic behaviors were observed depending on polymer concentration, shear rate, and shear history. The extract also displayed rod-climbing and self-siphoning properties typical of viscoelastic fluids. Such complex rheological properties have been reported in synthetic or chemically modified polymers but are less frequent in unmodified biopolymers. Although Mamaku extract obtained from the pith of the fern has been traditionally used by the Maori in New Zealand for treating wounds and diarrhea among other ailments, this material has never been characterized before. This study reports on the chemical composition of the extract and on its viscoelastic properties through rotational and oscillatory rheological measurements. Explanations of the mechanism behind the rheological properties were based on transient network models for associating polymers.