Sediments in coffee extracts: Composition and control by enzymatic hydrolysis

Evaluation of the thermal stability of bioactive compounds in coffee beans and their fractions modified in the roasting process

Coffee is used as flavor or health-promoting additive in thermally processed food. In this study, ground coffee and freeze-dried coffee extracts were evaluated in terms of their thermal stabilities, and for the first time heat resistance of fractions (mono-, dichlorogenic acids and caffeine) with different roasting levels was evaluated. It observed that the degradation of green coffee bean ingredients began at 150 °C, and for the re-heated light and dark roasted, in the range of 171-188 °C. The lyophilized extracts were more stable and their degradation began around 160 °C. However, with the re-treatment (cooking, baking, frying) of the coffee extract fractions, the degradation of the monochlorogenic acids commenced at 114 °C, while for dichlorogenics at 108 °C and caffeine at 146 °C. Monochlorogenic acids in Robusta coffee showed high antioxidant activity (55-70%) and the highest content of fiber (13-17%). Coffee could be used to fortify food.

Coffee cell walls—composition, influence on cup quality and opportunities for coffee improvements

The coffee beverage is the second most consumed drink worldwide after water. In coffee beans, cell wall storage polysaccharides (CWSPs) represent around 50 per cent of the seed dry mass, mainly consisting of galactomannans and arabinogalactans. These highly abundant structural components largely influence the organoleptic properties of the coffee beverage, mainly due to the complex changes they undergo during the roasting process. From a nutritional point of view, coffee CWSPs are soluble dietary fibers shown to provide numerous health benefits in reducing the risk of human diseases. Due to their influence on coffee quality and their health-promoting benefits, CWSPs have been attracting significant research attention. The importance of cell walls to the coffee industry is not restricted to beans used for beverage production, as several coffee by-products also present high concentrations of cell wall components. These by-products include cherry husks, cherry pulps, parchment skin, silver skin, and spent coffee grounds, which are currently used or have the potential to be utilized either as food ingredients or additives, or for the generation of downstream products such as enzymes, pharmaceuticals, and bioethanol. In addition to their functions during plant development, cell walls also play a role in the plant’s resistance to stresses. Here, we review several aspects of coffee cell walls, including chemical composition, biosynthesis, their function in coffee’s responses to stresses, and their influence on coffee quality. We also propose some potential cell wall–related biotechnological strategies envisaged for coffee improvements.

Effect of Processed Beverage By-Product-Based Diets on Biological Parameters, Conversion Efficiency and Body Composition of Hermetia illucens (L) (Diptera: Stratiomyidae)

Simple Summary

The Black Soldier Fly insect (BSF) Hermetia illucens (L.) (Diptera: Stratiomyidae) metabolizes low degraded ingredients and converts them into larval enriched nutrients. In the present study, the effect of processed beverage by-products, such as spent coffee grounds and brewer’s spent grains and their mixtures on biological parameters (larval development, survival), conversion efficiency and body composition of the BSF insect was evaluated. The effect of different rearing densities of BSF on the above parameters were also studied. Insect larvae were reared successfully in all tested diets, except for sole spent coffee grounds. Substrate mass reduction, protein conversion and bioconversion rates were higher on the reference feed, followed by brewer’s spent grains and brewer’s spent grains—spent coffee grounds mixture enriched with brewer’s yeast. Density did not affect any larval parameter except for fat. Our results illustrate that low value beverage by-products can be successfully utilized as constituents of a successful BSF diet.

Abstract

The effect of spent coffee grounds (SCG), brewer’s spent grains (BSG) and their mixtures with the addition of brewer’s yeast (BY) were tested in two rearing densities of the Black Soldier Fly, Hermetia illucens (L.). Different treatments were investigated on larval development, survival, yield, protein conversion (PrCR) and bioconversion rate (BCR), substrate mass reduction and body composition of the insect. BSF larvae were able to develop sufficiently in all diets, except on sole SCG. The addition of BY enhanced the performance properties of diets, especially in the case of SCG, where larvae underperformed. Substrate mass reduction, PrCR and BCR were affected only by feed and exhibited higher values on reference feed, followed by BSG and SCG+BSG enriched with BY. Density did not have a significant effect on various larval nutrients, except for fat, which was higher on larvae fed enriched feeds with BY and in the 300 larval density. The interaction between feed and density strongly affected the nitrogen and protein levels, larval yield and ash. Generally, diets which contained SCG exhibited high larval crude protein levels. Our results illustrate that low value beverage by-products can be successfully utilized as constituents of a successful BSF diet.

Isolation of proteins from spent coffee grounds. Polyphenol removal and peptide identification in the protein hydrolysates by RP-HPLC-ESI-Q-TOF

Several works have been focused on the extraction of polysaccharides, polyphenols and caffeine from spent coffee grounds (SCG) and their application in food formulations, but the peptide bioactivity from SCG protein hydrolysates has never been addressed. In the present work and for the first time, two different methods to isolate proteins from SCG have been compared, demonstrating that a urea-based extraction buffer provides a higher yield. This extraction method was then applied to compare the protein content in SCG from different coffee-brewing preparations, showing a higher protein content in SCG from espresso coffee machines. In addition, a polyphenol extraction step to remove interferences has been evaluated and the hydrolysis of the extracted proteins using alcalase and thermolysin enzymes has been compared. The effect of roasting degree on the antioxidant and in vitro angiotensin-converting enzyme (ACE)-inhibitory activity has been evaluated. The results show that the ACE-inhibitory activity is higher when SCG proteins are obtained from medium and dark roasted coffees and then hydrolyzed with thermolysin. Finally, the peptides contained in these hydrolysates have been identified by reversed-phase high-performance liquid chromatography coupled via electrospray ionization to a quadrupole time-of-flight mass spectrometer (RP-HPLC-ESI-Q-TOF).

Coffee-based colloids for direct solar absorption

Despite their promising thermo-physical properties for direct solar absorption, carbon-based nanocolloids present some drawbacks, among which the unpleasant property of being potentially cytotoxic and harmful to the environment. In this work, a sustainable, stable and inexpensive colloid based on coffee is synthesized and its photo-thermal properties investigated. The proposed colloid consists of distilled water, Arabica coffee, glycerol and copper sulphate, which provide enhanced properties along with biocompatibility. The photo-thermal performance of the proposed fluid for direct solar absorption is analysed for different dilutions and compared with that of a traditional flat-plate collector. Tailor-made collectors, opportunely designed and realized via 3D-printing technique, were used for the experimental tests. The results obtained in field conditions, in good agreement with two different proposed models, show similar performance of the volumetric absorption using the proposed coffee-based colloids as compared to the classical systems based on a highly-absorbing surface. These results may encourage further investigations on simple, biocompatible and inexpensive colloids for direct solar absorption.