The colloid and interface strategies to inhibit lipid digestion for designing low-calorie food.

Although fat is one of the indispensable components of food flavor, excessive fat consumption could cause obesity, metabolism syndromes and an imbalance in the intestinal flora. In the pursuit of a healthy diet, designing fat reducing foods by inhibiting lipid digestion and calorie intake is a promising strategy. Altering the gastric emptying rates of lipids as well as acting on the lipase by suppressing the enzymatic activity or limiting lipase diffusion via interfacial modulation can effectively decrease lipolysis rates. In this review, we provide a comprehensive overview of colloid-based strategies that can be employed to retard lipid hydrolysis, including pancreatic lipase inhibitors, emulsion-based interfacial modulation and fat substitutes. Plants-/microorganisms-derived lipase inhibitors bind to catalytic active sites and change the enzymatic conformation to inhibit lipase activity. Introducing oil-in-water Pickering emulsions into the food can effectively delay lipolysis via steric hindrance of interfacial particulates. Regulating stability and physical states of emulsions can also affect the rate of hydrolysis by altering the active hydrolysis surface. 3D network structure assembled by fat substitutes with high viscosity can not only slow down the peristole and obstruct the diffusion of lipase to the oil droplets but also impede the transportation of lipolysis products to epithelial cells for adsorption. Their applications in low-calorie bakery, dairy and meat products were also discussed, emphasizing fat intake reduction, structure and flavor retention and potential health benefits. However, further application of these strategies in large-scale food production still requires more optimization on cost and lipid reducing effects. This review provides a comprehensive review on colloidal approaches, design, principles and applications of fat reducing strategies to meet the growing demand for healthier diet and offer practical insights for the low-calorie food industry.

Ion-Induced Reassembly between Protein Nanotubes and Nanospheres.

Proteins used as building blocks to template nanostructures with manifold morphologies have been widely reported. Understanding their self-assembly and reassembly mechanism is important for designing functional biomaterials. Herein, we show that enzyme-hydrolyzed α-lactalbumin (α-lac) can self-assemble into either nanotubes in the presence of Ca2+ ions or nanospheres in the absence of Ca2+ in solution. Remarkably, such assembled α-lac nanotubes can be elongated by adding preassembled α-lac nanospheres and Ca2+ solution, which suggests that the self-assembled α-lac nanospheres undergo disassembly and reassembly processes into existing nanotube nuclei. By performing atomic force microscopy (AFM), transmission electron microscopy (TEM), and confocal laser scanning microscopy (CLSM), it indicates that there is an equilibrium among nanotubes, nanospheres, hydrolyzed α-lac, and Ca2+ in solution. The structural transition between nanotubes and nanospheres is driven from a less stable structure into a more stable structure determined by the conditions. During the transition from nanospheres into nanotubes, the hydrolyzed α-lac in nanospheres transfers into helical ribbon form at both nanotube extremities. Then helical ribbons close into mature nanotubes, extending the length of the initial nuclei. Besides, by dilution or adding ethylene glycol bis(2-aminoethyl ether) tetraacetic acid (EGTA), the decreased Ca2+ concentration in solution drives the Ca2+ dissociating from nanotubes into solution, leading to the transitions from nanotubes into nanospheres. The reversible transformation between nanotubes and nanospheres is achieved by adjusting the pH value from 7.5 to 5.0 and back to 7.5. This is because the stability of nanotubes decreases from pH 7.5 to 5 but increases from 5 to 7.5. Significantly, this approach can be used for the fabrication of various responsive nanomaterials from the same starting material.

Non-Cardiotoxic Tetradecanoic Acid-2,4-Dinitrophenol Ester Nanomicelles in Microneedles Exert Potent Anti-Obesity Effect by Regulating Adipocyte Browning and Lipogenesis.

Sustained oral uncoupler 2,4-dinitrophenol (DNP) administration exerts prominent anti-obesity effects, but the adipose tissue off-target disadvantage leads to systemic adverse effects. A novel non-cardiotoxicity DNP delivery method using a biocompatible microneedles patch containing the amphiphilic tetradecanoic acid-DNP ester (TADNP) is described, which is synthesized via esterification on the phenolic hydroxyl of DNP. The TADNP is self-assembled as nanomicelles, which enhance the endocytosis rate of DNP by adipocytes and its permeation in isolated adipose tissues. The microenvironment of adipose tissues promotes the massive release of DNP and plasma and simulated gastrointestinal fluids. The microneedles-delivered TADNP nanomicelles (MN-TADNP) effectively deliver DNP in treated adipose tissues and reduce DNP content in off-target organs. Both oral and MN patch-delivered TADNP micelles effectively exert anti-obesity effects in a mouse model of high-fat diet-induced obesity; and noteworthily, MN-TADNP exhibit more satisfactory biosafety than oral administration. Here, a smart MN patch loaded with tetradecanoic acid-modified DNP is reported, which enhances its accumulation in adipose tissues and exerts an anti-obesity effect without causing any systemic toxicity.

The fortification of encapsulated soy isoflavones and texture modification of soy milk by α-lactalbumin nanotubes.

Nanocarriers can improve the dispersibility of hydrophobic bioactive compounds and potentially improve the texture of liquid food formulations. Here, nanotubes (NTs) with a high aspect ratio formed by self-assembly of peptides partially hydrolyzed from α-lactalbumin (α-lac) were used to deliver soy isoflavones (IFs) and modify soy milk texture. IFs encapsulated by nanotube (NT/IFs) via hydrophobic interactions, which had improved dispersibility, with a maximum loading efficiency of 4%. The rheological characterization showed that the nanotubes enhanced the viscoelastic property and long term-stability of soy milk. About 80% of the NT/IFs in soy milk survived simulated in in vitro gastric digestion promoting the release of IFs in the intestinal phase. Overall, this work demonstrated that α-lac nanotubes may be a multi-functional carrier system for hydrophobic compounds providing beneficial changes to functional food texture.

The intracellular fate and transport mechanism of shape, size and rigidity varied nanocarriers for understanding their oral delivery efficiency.

Nanocarriers have become an effective strategy to overcome epithelial absorption barriers. During the absorption process, the endocytosis mechanisms, cell internalization pathways, and transport efficiency of nanocarriers are greatly impacted by their physical properties. To understand the relationship between physical properties of nanocarriers and their abilities overcoming multiple absorption barriers, nanocarriers with variable physical properties were prepared via self-assembly of hydrolyzed α-lactalbumin peptide fragments. The impacts of size, shape, and rigidity of nanocarriers on epithelial cells endocytosis mechanisms, internalization pathways, transport efficiency, and bioavailability were studied systematically. The results showed that nanospheres were mainly internalized via clathrin-mediated endocytosis, which was then locked in lysosomes and degraded enzymatically in cytoplasm. While macropinocytosis was the primary pathway of nanotubes and transported to the endoplasmic reticulum and Golgi apparatus, resulting in a high drug concentration and sustained release in cytoplasm. Besides, nanotubes can overcome the multi-drug resistance by inhibiting the P-glycoprotein efflux. Furthermore, nanotubes can open intercellular tight-junctions instantaneously and reversibly, which promotes transport into blood circulation. The aqueous solubility of hydrophobic bioactive mangiferin (Mgf) was improved by nanocarriers. Most importantly, the bioavailability of Mgf was the highest for cross-linked short nanotube (CSNT) which outperformed free Mgf and other formulations by in vivo pharmacokinetic studies. Finally, Mgf-loaded CSNT showed an excellent therapeutic efficiency in vivo for the intervention of streptozotocin-induced diabetes. These results indicate that cross-linked α-lactalbumin nanotubes could be an effective nanocarrier delivery system for improving the epithelium cellular absorption and bioavailability of hydrophobic bioactive compounds.

The stability and spicy taste masking effect of capsaicin loaded α-lactalbumin micelles formulated in defatted cheese.

Capsaicin (Cap) is a promising bioactive compound having many health-promoting benefits. However, it is difficult to be applied in food due to its poor aqueous solubility, low stability and bioavailability. Besides, its strong spicy taste and irritation to the gastrointestinal tract further limit the application of Cap in food. To solve this problem, Cap was loaded into a self-assembled nanocarrier formed by partial hydrolysis of α-lactalbumin (α-lac). The Cap was successfully loaded into the 21.2 nm micelles with a loading capacity of 123.4 ± 6.1 mg g-1. The aqueous solubility was greatly improved. Besides, nanomicelles also showed intestinal responsive release behavior. The in vivo bioavailability of Cap was improved by nanomicelles for 3.1 times. The Cap loaded nanomicelles in the milk system showed good colloidal stability compared to solely Cap in milk. Therefore, the Cap loaded nanocarriers were added into the de-fatted milk to prepare de-fatted cheese with an acceptable spicy flavor. The nanocarriers were clearly captured in the cheese casein network as confirmed by confocal microscopy. The sensory evaluation results showed the spicy taste of capsaicin was reduced in the nanomicelle system and further reduced in the nanomicelle-cheese systems. We postulated that it might be due to the nanomicelles reducing the contact of capsaicin with sensory neurons in the tongue thus masking the spicy taste. The cheese casein network structure further masked their contact. The above results indicated that Cap embedding via α-lac nanocarriers was feasible for masking their spicy taste and applying Cap to food systems such as milk and cheese.

On demand regulation of blood glucose level by biocompatible oxidized starch-Con A nanogels for glucose-responsive release of exenatide.

Diabetes mellitus is a long-term chronic disease characterized by abnormal high level blood glucose (BG). An artificial closed-loop system that mimics pancreatic ß-cells and releases insulin on demand has potential to improve the therapeutic efficiency of diabetes. Herein, a lectin Concanavalin A modified oxidized starch nanogel was designed to regulate glucose dynamically according to different glucose concentrations. The nanogels were formed by double cross-linking the Concanavalin A and glucose units on oxidized starch via specific binding and amide bonds to achieve the high drug loading and glucose responsiveness. The results showed that oxidized starch nanogels prolonged the half-life of antidiabetic peptide drug exenatide and released it in response to high BG concentrations. It could absorb BG at a high level and maintain glucose homeostasis. Besides, the oxidized starch nanogels performed well in recovering regular BG level from hyperglycemia state and maintaining in euglycemia state that fitted in a biological rhythm. In addition, the nanogels showed high biocompatibility in vivo and could improve plasma half-life and therapeutic efficacy of exenatide. Overall, the nanogels protected peptide drugs from degradation in plasma as a glucose-responsive platform showing a high potential for peptide drugs delivery and antidiabetic therapy.

The kinetic mechanism of cations induced protein nanotubes self-assembly and their application as delivery system.

The amphiphilic proteins can be used as building blocks (BBs) forming various self-assemblies. Understanding their self-assembly mechanism is important for designing novel nanomaterials. Herein, the BBs dimers were first prepared from carboxyl-abundant enzymolyzed α-lactalbumin (α-lac) at 50 °C. Then the unidentate coordination of Ca2+ between the BBs caused a ß-sheet stacking to further self-assemble into nanotubes (NTs). Compared with the traditional "one-pot" method, a step-wise new method was applied to study hydrolysis, aggregation and self-assembly processes separately. The α-lac was hydrolyzed into 11 kDa amphiphilic peptides independent of temperature while a BBs dimer was formed at 50 °C by hydrophobic interaction. Ca2+ induced a conformational change of BBs and promoted these BBs gradually aggregate into 10 strands of filaments, which twisted into helical ribbons by electrostatic repulsion. Ca2+ further induced the twisted helical ribbons closed into NTs driven by the reduction of line tension energy. Besides, the carboxyl-Ca2+ coordination dominated NTs elongation in the longitudinal direction and filaments aggregation in the lateral direction with the same binding stoichiometry of 1:1 respectively. Finally, NTs successfully encapsulated curcumin and improved the viscosity of liquid food. α-Lac NTs show a high potential as a delivery system for food applications.

Intestinal-targeted nanotubes-in-microgels composite carriers for capsaicin delivery and their effect for alleviation of Salmonella induced enteritis.

Salmonella is a word-wide food-borne pathogen, which can cause severe enteritis and intestinal microbiota imbalance. Capsaicin (Cap), a food-based bioactive ingredient, has antibacterial and anti-inflammatory properties. However, its low solubility, low bioavailability and the irritation to digestive tract greatly limit its applications. Here, an intestinal responsively "nanotubes-in-microgel" composite carrier was constructed by capturing α-lactalbumin (α-lac) nanotubes in low-methoxy pectin microgels (LMP-NT) (52 µm). Cap was loaded in such system via hydrophobic interaction with a loading capacity of 38.02 mg/g. The LMP microgels remained stable and protected NT/Cap from early releasing in the gastric condition. It showed an excellent mucoadhesive capacity, which can prolong the intestinal retention up to 12 h and control release NT/Cap in intestine. Afterward, NT/Cap could penetrate across the mucus layer deeply and enter the intestinal villi epithelial cells efficiently. LMP-NT microgels achieved a mucoadhesive-to-penetrating transition in response to intestinal pH, improving the epithelium absorption and the in vivo bioavailability of Cap. Oral administration of LMP-NT/Cap could effectively alleviate enteritis caused by Salmonella infection and maintain the homeostasis of gut microbiota. Overall, this work suggested that LMP-NT composite microgels were promising for intestine-targeted and oral delivery of hydrophobic bioactive food compounds.

Hydrolysis and oxidation of protein and lipids in dry-salted grass carp (Ctenopharyngodon idella) as affected by partial substitution of NaCl with KCl and amino acids.

To obtain healthier meat products with reduced Na content, the salt substitute containing l-histidine and l-lysine was compared with NaCl in the hydrolysis and oxidation of protein and lipids of dry-salted fish during processing. Compared with NaCl-treated fish (S-F), salt substitute treated fish (SS-F) had a lower Na content, higher moisture content and lower hardness. Sensory analysis showed that salt substitute didn't affect the acceptability of salted fish. The free fatty acids of SS-F treated fish had a slight tendency toward lipolysis at the end of processing. Additionally, the conjugated diene value, lipoxygenase activity and malondialdehyde value were lower in the ventral and dorsal muscles for the SS-F treatment. Meanwhile, the protein carbonyls and thiol groups were significantly decreased as cathepsin B and L activities and FAA content were increased in the ventral and dorsal muscles for the SS-F treatment. l-Histidine and l-lysine accelerated the hydrolysis (inhibit the oxidation) of protein and lipids in dry-salted grass carp, illustrating that l-histidine and l-lysine will be a positive approach to develop healthier meat products.