Effect of green tea catechins on physical stability and sensory quality of lactose-reduced UHT milk during storage for one year

Multifaceted roles of foam-mat freeze-dried catechins nanoencapsulation to enhance catechins stability and bioaccessibility, and quality of green tea catechins-fortified milk

Catechins, widely used as functional ingredients and health supplements, face usage limitations due to their poor stability and bioaccessibility. In this study, encapsulation techniques including nanoemulsion and foam-mat freeze-drying were utilized to enhance the stability and bioaccessibility of catechins. Catechins nanoemulsion (CaNE) was ultrasonically fabricated and foam-mat freeze-dried CaNE (FD-CaNE) was prepared by mixing with a blend of maltodextrin and gum arabic as wall material and foaming with hydroxypropyl methylcellulose before freeze drying. Unencapsulated catechins (UN-Ca), CaNE, and FD-CaNE were fortified in pasteurized milk to improve its functional properties. FD-CaNE was shown to be the best at preserving total flavonoid content (TFC) and catechins' antioxidant activity (AA), retarding lipid oxidation, and inhibiting bacterial growth. In vitro gastrointestinal digestion test, digested CaNE and FD-CaNE showed better bioaccessibility of catechins by having higher percentage of TFC recovery and AA than the digested UN-Ca. This study has proved that FD-CaNE can be used as bioactive food ingredients to enhance the stability and bioaccessibility of catechins in food matrices and digestive system, and to improve quality and shelf life of catechins-fortified milk.

2-Heptanone, 2-nonanone, and 2-undecanone confer oxidation off-flavor in cow milk storage

Flavor sensation is one of the most prevalent characteristics of food industries and an important consumer preference regulator of dairy products. So far, many volatile compounds have been identified, and their molecular mechanisms conferring overall flavor formation have been reported extensively. However, little is known about the critical flavor compound of a specific sensory experience in terms of oxidized off-flavor perception. Therefore, the present study aimed to compare the variation in sensory qualities and volatile flavors in full-fat UHT milk (FFM) and low-fat UHT milk (LFM) samples under different natural storage conditions (0, 4, 18, 25, 30, or 37°C for 15 and 30 d) and determine the main component causing flavor deterioration in the FFM and LFM samples using sensory evaluation, electronic nose, and headspace solid-phase microextraction-gas chromatography-mass spectrometry (HS-SPME-GC-MS). In addition, the Pearson correlation between the volatile flavor components and oxidative off-flavors was analyzed and validated by sensory reconstitution studies. Compared with the LFM samples, the FFM samples showed a higher degree of quality deterioration with increased storage temperature. Methyl ketones of odd carbon chains (i.e., 2-heptanone, 2-nonanone, 2-undecanone, 2-tridecanone, and 2-pentadecanone) reached a maximum content in the FFM37 samples over 30 d storage. The combined results of the Pearson correlation and sensory recombination study indicated that 2-heptanone, 2-nonanone, and 2-undecanone conferred off-flavor perception. Overall, the present study results provide potential target components for detecting and developing high-quality dairy products and lay a foundation for specific sensory flavor compound exploration in the food industry.

Dietary polyphenols: regulate the advanced glycation end products-RAGE axis and the microbiota-gut-brain axis to prevent neurodegenerative diseases

Advanced glycation end products (AGEs) are formed in non-enzymatic reaction, oxidation, rearrangement and cross-linking between the active carbonyl groups of reducing sugars and the free amines of amino acids. The Maillard reaction is related to sensory characteristics in thermal processed food, while AGEs are formed in food matrix in this process. AGEs are a key link between carbonyl stress and neurodegenerative disease. AGEs can interact with receptors for AGEs (RAGE), causing oxidative stress, inflammation response and signal pathways activation related to neurodegenerative diseases. Neurodegenerative diseases are closely related to gut microbiota imbalance and intestinal inflammation. Polyphenols with multiple hydroxyl groups showed a powerful ability to scavenge ROS and capture α-dicarbonyl species, which led to the formation of mono- and di- adducts, thereby inhibiting AGEs formation. Neurodegenerative diseases can be effectively prevented by inhibiting AGEs production, and interaction with RAGEs, or regulating the microbiota-gut-brain axis. These strategies include polyphenols multifunctional effects on AGEs inhibition, RAGE-ligand interactions blocking, and regulating the abundance and diversity of gut microbiota, and intestinal inflammation alleviation to delay or prevent neurodegenerative diseases progress. It is a wise and promising strategy to supplement dietary polyphenols for preventing neurodegenerative diseases via AGEs-RAGE axis and microbiota-gut-brain axis regulation.

Effects of Momordica cochinchinensis Aril Extract on Sterilized Low-Fat Milk, Antioxidant and Antiproliferative Activities

The aril extract (0.4% g/mL) of Gac fruit in milk supplement can inhibit cancer cell lines. Moreover, the extract has no toxicity against normal cells. In a sensory test, sterilized low-fat milk supplemented with 0.4% extract did not have different sensory score compared to the control. During the sterilization process, extract was not significantly different from the control. In sterilization (121°C, 15 min), adding Gac fruit extract in low-fat milk results in antioxidant activity increase. The extract increased values for the redness and yellowness of sterilized low fat, but the lightness decreased. Also, the extract slightly decreased the alcohol stability of sterilized low-fat milk. At an accelerated rate (50°C, 28 days), there was no effect of the extract addition on protein aggregation in low-fat milk. Moreover, the TBA values indicate the ability of the extract to inhibit lipid oxidation. Finally, Gac fruit extract added to milk may possibly extend the shelf life of sterilized low-fat milk and improve its antioxidant and anticancer activity properties.

Understanding the effect of storage temperature on the quality of semi-skimmed UHT hydrolyzed-lactose milk: an insight on release of free amino acids, formation of volatiles organic compounds and browning

Proteolytic side activity of the lactase preparations (LPs) intended for ultra-high temperature hydrolyzed-lactose milk (UHLM) production induces changes in the product quality during shelf-life. The problem is particularly relevant when the enzyme is added aseptically in the packaging ("in pack" process), while the negative quality effects can be mitigated following the "in batch" process adding the LP before thermal sterilization. In this study, we monitored the quality over time of UHLM produced "in batch" and stored at 4, 20, 30 and 40 °C focusing on proteolysis, volatiles organic compounds (VOCs) formation and color changes. The goal was to identify the key reactions and compounds relevant for the product quality. An increase in storage temperature determined significant changes in the free amino acids profile increasing Strecker aldehydes and methyl ketones formation. At 30 and 40 °C, Maillard reaction and lipid oxidation ended up in a modification of the milk color, whereas at 4 and 20 °C no significant alteration was observed. Altogether, the results suggested a coordinate involvement of Maillard reaction, protein and lipid oxidation to milk browning and off-flavors formation in UHLM.

Green Tea Extract Decreases Arg-Derived Advanced Glycation Endproducts but Not Lys-Derived AGEs in UHT Milk during 1-Year Storage

Epigallocatechin gallate (EGCG)-enriched green tea extract (GTE) was added to lactose-reduced UHT-treated milk to evaluate its role in perturbing the Maillard reaction and the formation of advanced glycation endproducts (AGEs) during 1-year storage. The UHT processing caused epimerization of EGCG into gallocatechin gallate (GCG). For milk samples with added 0.1% w/v GTE, a EGCG/GCG loss of 26% was found soon after the UHT treatment and the loss increased to 64% after the 1-year of storage. LC-MS/MS analysis revealed the presence of various EGCG/GCG-α-dicarbonyl adducts and EGCG/GCG-hydroxymethylfurfural adducts in milk samples, while EGCG/GCG-amino acid adducts were not detected. Although EGCG/GCG trapped α-dicarbonyl compounds including glyoxal, methylglyoxal, 3-deoxyglucosone/3-deoxygalactosone, and diacetyl, it did not lower their net steady-state concentrations, except of 3-deoxyglucosone. The addition of GTE reduced the formation of Arg-derived AGEs by 2- to 3-fold, but surprisingly enhanced the accumulation of furosine and lysine-derived AGEs [Nε-(carboxymethyl)lysine and Nε-(carboxyethyl)lysine)] by 2-4-fold depending on the concentration of the added GTE and storage time. The present study shows that trapping of α-dicarbonyl compounds by EGCG may not be the major pathway for inhibiting the formation of AGEs in milk.

Trapping of Carbonyl Compounds by Epicatechin: Reaction Kinetics and Identification of Epicatechin Adducts in Stored UHT Milk

The kinetics of the reaction between epicatechin and various carbonyl compounds typically formed in cooked and stored foods were evaluated in model systems at pH 7.4 and 37 °C, and the corresponding reaction products in stored ultrahigh temperature (UHT) milk-added epicatechin were identified by high-performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS). The rate constants for the reactions of carbonyl compounds with epicatechin decreased in the following the order: methylglyoxal; 1.6 ± 0.2 M^-1 s^-1 > glyoxal; (5.9 ± 0.3) × 10^-2 M^-1 s^-1 ≥ 5-(hydroxymethyl)furfural; (4.0 ± 0.2) × 10^-2 M^-1 s^-1 ≥ acetaldehyde; (2.6 ± 0.3) × 10^-2 M^-1 s^-1 ≥ phenylacetaldehyde; (2.1 ± 0.2) × 10^-2 M^-1 s^-1 ≥ furfural; (4.3 ± 0.1) × 10^-3 M^-1 s^-1 > 2-methylbutanal and 3-methylbutanal; ∼0 M^-1 s^-1. Reaction products generated by epicatechin and methylglyoxal, glyoxal, 5-(hydroxymethyl)furfural, and acetaldehyde were detected in UHT milk samples by incubating milk samples with epicatechin at 37 °C for 24 h. The lack of reaction between epicatechin and phenylacetaldehyde, furfural, 2-methylbutanal, and 3-methylbutanal in stored UHT milk may be due to their slow reaction rates or low concentration in stored UHT milk. It is demonstrated that epicatechin traps 5-(hydroxymethyl)furfural, acetaldehyde, glyoxal, and methylglyoxal and may thereby reduce off-flavor formation in UHT milk during storage both by trapping of precursors (methylglyoxal and glyoxal) for off-flavor formation and by direct trapping of off-flavors.

Chemical and sensory changes during shelf-life of UHT hydrolyzed-lactose milk produced by "in batch" system employing different commercial lactase preparations

Manufacturing shelf-stable Ultra-high temperature hydrolyzed-lactose milk (UHLM) is a challenge for dairy producers, as the product undergoes chemical changes during storage due to both reducing sugars reactivity and proteolysis arising from the impurity of the lactase preparations. In the present study, the "in batch" production system, which includes the addition of the lactase before the thermal treatment, was demonstrated a valuable alternative to the more popular "in pack" system, where lactase is added directly into each milk package after thermal sterilization. The features of the technology were investigated by monitoring the changes in free amino acids, volatile organic compounds, color and sensory properties of UHLMs produced with three different lactase preparations (LPs), up to 120 days at 20 °C. Upon UHT processing, the proteolytic side activity of lactases was minimized, so minimum breakdown of milk protein was achieved. The release of free amino acids was dependent on the lactase purity only in the early production phases, whereas it did not change over time. The Strecker aldehydes benzaldehyde and 2-methylbutanal resulted as effective markers to correlate with the initial lactase purity during storage. Color and sensory slightly changed during storage but were poorly correlated with the different lactases, resembling to phenomena typical of milk aging. This latter result suggested that production costs might be lowered by opting for less-purified lactases when considering the "in batch" technology, supporting the application of this production system for the design of UHLM with high-quality standards and low risk of alterations during shelf-life.

Tea from the Food Science Perspective: An Overview

Tea (Camelia sinensis L.) is one of the main beverages known and consumed all around the world. Quality of tea is not only linked to the raw material but also to the processing steps that influence on the biochemical and sensory characteristics of each type of tea. This overview is focused on the differences in the production and composition of the main types of teas present in the market, highlighting not only their chemical and sensory characteristics, but also the importance of this plant from the food science viewpoint related to its several applications.