Enzymatic Browning in Sugar Beet Leaves (Beta vulgaris L.): Influence of Caffeic Acid Derivatives, Oxidative Coupling, and Coupled Oxidation.

Sugar beet (Beta vulgaris L.) leaves of 8 month (8m) plants showed more enzymatic browning than those of 3 month (3m). Total phenolic content increased from 4.6 to 9.4 mg/g FW in 3m and 8m, respectively, quantitated by reverse-phase-ultrahigh-performance liquid chromatography-ultraviolet-mass spectrometry (RP-UHPLC-UV-MS). The PPO activity was 6.7 times higher in extracts from 8m than from 3m leaves. Substrate content increased from 0.53 to 2.45 mg/g FW in 3m and 8m, respectively, of which caffeic acid glycosyl esters were most important, increasing 10-fold with age. Caffeic acid glycosides and vitexin derivatives were no substrates. In 3m and 8m, nonsubstrate-to-substrate ratios were 8:1 and 3:1, respectively. A model system showed browning at 3:1 ratio due to formation of products with extensive conjugated systems through oxidative coupling and coupled oxidation. The 8:1 ratio did not turn brown as oxidative coupling occurred without much coupled oxidation. We postulate that differences in nonsubstrate-to-substrate ratio and therewith extent of coupled oxidation explain browning.

Effect of Plant Age on the Quantity and Quality of Proteins Extracted from Sugar Beet (Beta vulgaris L.) Leaves.

Effects of the developmental stage (e.g., young, mature, or senescent) of leaves on their chemical composition have been described in the literature. This study focuses on the variation in chemical composition and quantity and quality of proteins extracted from leaves due to variation in plant age (i.e., harvesting time), using leaves from sugar beets grown in a field (Rhino, Arrival) and in a greenhouse (Isabella). Within the same variety (Rhino, field; Arrival, field; Isabella, greenhouse) the protein content was similar for leaves from young and old plants (22 ± 1, 16 ± 1, and 10 ± 3% w/w db, respectively). Variation in final protein isolation yield was mostly due to variation in nitrogen extractability (28-56%), although no consistent correlation with plant age was found. A significant effect of plant age was observed on the quality (color) of the extracted protein, that is, brown (indicative of polyphenol oxidase activity) and yellow for extracts from old and young plants, respectively.

Minced beef is more rapidly digested and absorbed than beef steak, resulting in greater postprandial protein retention in older men.

BACKGROUND: Older individuals generally experience a reduced food-chewing efficiency. As a consequence, food texture may represent an important factor that modulates dietary protein digestion and absorption kinetics and the subsequent postprandial protein balance. OBJECTIVE: We assessed the effect of meat texture on the dietary protein digestion rate, amino acid availability, and subsequent postprandial protein balance in vivo in older men. DESIGN: Ten older men (mean ± SEM age: 74 ± 2 y) were randomly assigned to a crossover experiment that involved 2 treatments in which they consumed 135 g of specifically produced intrinsically L-[1-(13)C]phenylalanine-labeled beef, which was provided as beef steak or minced beef. Meat consumption was combined with continuous intravenous L-[ring-(2)H5]phenylalanine and L-[ring-(2)H2]tyrosine infusion to assess beef protein digestion and absorption kinetics as well as whole-body protein balance and skeletal muscle protein synthesis rates. RESULTS: Meat protein-derived phenylalanine appeared more rapidly in the circulation after minced beef than after beef steak consumption (P < 0.05). Also, its availability in the circulation during the 6-h postprandial period was greater after minced beef than after beef steak consumption (61 ± 3% compared with 49 ± 3%, respectively; P < 0.01). The whole-body protein balance was more positive after minced beef than after beef steak consumption (29 ± 2 compared with 19 ± 3 µmol phenylalanine/kg, respectively; P < 0.01). Skeletal muscle protein synthesis rates did not differ between treatments when assessed over a 6-h postprandial period. CONCLUSIONS: Minced beef is more rapidly digested and absorbed than beef steak, which results in increased amino acid availability and greater postprandial protein retention. However, this does not result in greater postprandial muscle protein synthesis rates. This trial was registered at clinicaltrials.gov as NCT01145131.

The muscle protein synthetic response to the combined ingestion of protein and carbohydrate is not impaired in healthy older men.

Aging is associated with a progressive decline in skeletal muscle mass. It has been hypothesized that an attenuated muscle protein synthetic response to the main anabolic stimuli may contribute to the age-related loss of muscle tissue. The aim of the present study was to compare the muscle protein synthetic response following ingestion of a meal-like amount of dietary protein plus carbohydrate between healthy young and older men. Twelve young (21 ± 1 years) and 12 older (75 ± 1 years) men consumed 20 g of intrinsically L-[1-(13)C]phenylalanine-labeled protein with 40 g of carbohydrate. Ingestion of specifically produced intrinsically L-[1-(13)C]phenylalanine-labeled protein allowed us to assess the subsequent incorporation of casein-derived amino acids into muscle protein. Blood samples were collected at regular intervals, with muscle biopsies obtained prior to and 2 and 6 h after protein plus carbohydrate ingestion. The acute post-prandial rise in plasma glucose and insulin concentrations was significantly greater in the older compared with the younger males. Plasma amino acid concentrations increased rapidly following drink ingestion in both groups. However, plasma leucine concentrations were significantly lower at t = 90 min in the older when compared with the young group (P < 0.05). Muscle protein-bound L-[1-(13)C]phenylalanine enrichments increased to 0.0071 ± 0.0016 and 0.0072 ± 0.0013 mole percent excess (MPE) at 2 h and 0.0229 ± 0.0016 and 0.0213 ± 0.0024 MPE at 6 h following ingestion of the intrinsically labeled protein in the young and older males, respectively, with no differences between groups (P > 0.05). We conclude that the use of dietary protein-derived amino acids for muscle protein synthesis is not impaired in healthy older men following intake of protein plus carbohydrate.

Anti-inflammatory effects of a special carbohydrate-whey protein cake after exhaustive cycling in humans.

Intense exercise induces increased levels of pro-inflammatory and anti-inflammatory cytokines. Thus, the purpose of this study was to examine the effects of a special cake (consisting of carbohydrate to whey protein 3.5:1) vs. an isocaloric carbohydrate cake on inflammatory markers after exhaustive cycling in humans. Nine subjects received either the experimental or placebo cake in a counterbalanced fashion using a crossover, double-blind, repeated-measures design. They performed one trial involving a 2h exercise on a cycle ergometer at 60-65% VO2max followed by a 4h recovery and then a second trial involving an 1h exercise at 60-65% VO2max which was increased at 95% VO2max. Blood samples were collected pre-exercise, 30 min and 4h post-exercise, post-time Trial and 48 h post-time Trial. Cakes were consumed immediately post-exercise and every 1h for the next 3h. The results showed that consumption of the experimental cake reduced significantly (p<0.05), 4h post-exercise, the pro-inflammatory protein levels IL-6 and CRP compared to the control group by 50% and 46% respectively. Moreover, in the experimental cake group, the level of the anti-inflammatory cytokine IL-10 was higher by 118%, 4h post-exercise, compared to the control group but not statistically significant.

Carbohydrate co-ingestion with protein does not further augment post-prandial muscle protein accretion in older men.

BACKGROUND: A blunted muscle protein synthetic response to protein ingestion may contribute to the age related loss of muscle tissue. We hypothesized that the greater endogenous insulin release following co-ingestion of carbohydrate facilitates post-prandial muscle protein accretion after ingesting a meal-like bolus of protein in older males. METHODS: Twenty-four healthy older men (75±1 y) were randomly assigned to ingest 20 g intrinsically L-[1-13C] phenylalanine-labeled casein protein with (PRO-CHO) or without (PRO) 40 g carbohydrate. Ingestion of specifically produced intrinsically L-[1-13C] phenylalanine labeled protein allowed us to assess post-prandial incorporation of dietary protein derived amino acids into muscle protein. Blood samples were collected at regular intervals, with muscle biopsies being obtained prior to and 2 and 6 h after protein ingestion. RESULTS: Plasma glucose and insulin concentrations showed a greater increase in PRO-CHO compared with PRO (P<0.001). Muscle protein-bound L-[1-13C] phenylalanine enrichments tended to increase to a greater extent in PRO-CHO compared with PRO during the first 2 h after protein ingestion (0.0072±0.0013 vs 0.0046±0.010 MPE, respectively; P=0.13). However, 6 h after protein ingestion, differences in muscle protein-bound L-[1-13C] phenylalanine enrichments were no longer observed between experiments (0.0213±0.0024 vs 0.0185±0.0010 MPE, respectively; P=0.30). CONCLUSIONS: This study shows that carbohydrate ingestion may accelerate, but does not further augment post-prandial incorporation of dietary protein derived amino acids into muscle protein in healthy elderly men.

Leucine co-ingestion improves post-prandial muscle protein accretion in elderly men.

BACKGROUND & AIMS: It has been speculated that the amount of leucine in a meal largely determines the post-prandial muscle protein synthetic response to food intake. The present study investigates the impact of leucine co-ingestion on subsequent post-prandial muscle protein accretion following the ingestion of a single bolus of dietary protein in elderly males. METHODS: Twenty-four elderly men (74.3±1.0 y) were randomly assigned to ingest 20 g intrinsically L-[1-(13)C]phenylalanine-labeled casein protein with (PRO+LEU) or without (PRO) 2.5 g crystalline leucine. Ingestion of specifically produced intrinsically labeled protein allowed us to create a plasma phenylalanine enrichment pattern similar to the absorption pattern of phenylalanine from the ingested protein and assess the subsequent post-prandial incorporation of L-[1-(13)C] phenylalanine into muscle protein. RESULTS: Plasma amino acid concentrations increased rapidly following protein ingestion in both groups, with higher leucine concentrations observed in the PRO+LEU compared with the PRO group (P<0.01). Plasma L-[1-(13)C]phenylalanine enrichments increased rapidly and to a similar extent in both groups following protein ingestion. Muscle protein-bound L-[1-(13)C]phenylalanine enrichments were significantly greater after PRO+LEU when compared with PRO at 2 h (72%; 0.0078±0.0010 vs. 0.0046±0.00100 MPE, respectively; P<0.05) and 6 h (25%; 0.0232±0.0015 vs. 0.0185±0.0010 MPE, respectively; P<0.05) following protein ingestion. The latter translated into a greater muscle protein synthetic rate following PRO+LEU compared with PRO over the entire 6 h post-prandial period (22%; 0.049±0.003 vs. 0.040±0.003% h(-1), respectively; P<0.05). CONCLUSION: Leucine co-ingestion with a bolus of pure dietary protein further stimulates post-prandial muscle protein synthesis rates in elderly men.

Effect of a special carbohydrate-protein cake on oxidative stress markers after exhaustive cycling in humans.

Exercise has been associated with oxidative stress that is correlated with muscle fatigue and reduced exercise performance. The aim of this study was to examine the effects of a special cake (consisting of carbohydrate to whey protein 3.5:1) vs an isocaloric carbohydrate cake on biomarkers of oxidative stress in 9 males after exhaustive cycling. A randomized single-blind cross-over study was completed. They performed one trial involving a 2-h exercise on a cycle ergometer at 60-65% VO(2)max followed by a 4-h recovery and then a second trial involved an 1-h exercise at 60-65% VO(2)max which was increased at 95% VO(2)max (time trial). The subjects received 4 experimental or placebo cakes after the first trial (the first immediately after and then one every hour). Blood samples were collected at eight time intervals: pre-exercise, 30 min, 1.5 h and 4 h post-exercise, post time Trial, 1 h, 24 h and 48 h post time Trial. Thiobarbituric Acid Reactive Substances (TBARS), protein carbonyls, total antioxidant capacity (TAC), catalase and glutathione (GSH) were determined spectrophotometrically. The mean time to exhaustion did not differ upon cake consumption. Consumption of the special cake reduced TBARS significantly, but had no effect on other oxidative stress markers.

Effect of different iron compounds on wheat and gluten-free breads.

BACKGROUND: Iron fortification of bread often results in sub-optimal quality of the final product due to undesirable changes in the physical characteristics and sensory properties of the bread. In this study both the form of iron (soluble, insoluble or encapsulated) and the type of bread (wheat or gluten-free) were varied in order to investigate the effect of iron and gluten on the product characteristics. RESULTS: The effect of iron on the quality characteristics of the breads investigated depended on iron type, but not on iron solubility. Colour, crust firmness, specific volume, cell number and uniformity as well as aroma were the attributes that were mainly affected in iron-enriched wheat bread. In some cases, specific volume was 30% lower than that of the control sample, while cell uniformity was significantly lower, as low as 50% of the control sample in some fortified samples. In gluten-free breads, differences between unfortified and fortified samples included colour, crust firmness, cell number, 'moisture' odour, metallic taste and stickiness. In some cases, the sensory scores were better for fortified samples. CONCLUSIONS: Differences due to iron fortification were less pronounced in gluten-free compared to wheat breads. The choice of the appropriate iron compound which will not cause adverse quality changes is still a challenge.