Ombretta Marconi

Characterization of the volatile profiles of beer using headspace solid-phase microextraction and gas chromatography-mass spectrometry.

BACKGROUND The objective of this study was a multivariate characterization of the volatile profile of beers. Such a characterization is timely considering the increasing worldwide consumption of beer, the continuous growth of microbreweries and the importance of volatile compounds to beer flavour. A method employing solid-phase microextraction and gas chromatography-mass spectrometry (SPME-GC-MS) was optimized and then applied to a sample set of 36 industrial and craft beers of various styles and fermentation types. RESULTS The volatile profiles of different beer styles is described, with particular attention paid to the volatile compounds characteristic of a spontaneously fermented lambic raspberry framboise beer. Furthermore, it was also possible to identify which specific volatile compounds are principally responsible for the differences in the volatile profiles of top- and bottom-fermented beers. Moreover, a volatile fingerprint of the craft top-fermented Italian beers was defined, as they show a very similar volatile profile. Finally, the volatile compounds that are characteristic of the bock-style beers are described. CONCLUSIONS The SPME-GC-MS analytical method optimized in this study is suitable for characterizing the volatile fingerprint of different beers, especially on the basis of the kind of fermentation (top, bottom or spontaneous), the method of production and the style of the beer.

Production of alcohol-free beer

With greater interest in health and concern about weight and considering the warnings about alcohol abuse, especially when driving, consumer preference for low-alcohol and alcohol-free beer is increasing, but the definitions of “low-alcohol” and “alcohol-free” beers vary in different countries as well as their composition. Low-alcohol or any other word or description which implies that the drink being described is low in alcohol may not be applied to any alcoholic drink unless: (a) the drink has an alcoholic strength by volume of not more than 1.2% and (b) the drink is marked or labeled with an indication of its maximum alcoholic strength immediately preceded by the word “not more than.” The most common way to produce non-alcoholic beers is to modify the normal brewing process so that fermentation is limited and almost no ethanol is produced. There are several techniques for determining alcohol concentration by controlling the extent of fermentation. Moreover, beers produced in a traditional way and in different brands can be made alcohol-free by using physical methods to remove the alcohol at the end of the production process. The biological methods used to produce alcohol-free beers do not usually require special extra plant, but rather a more accurately controlled process to prevent an overproduction of alcohol.

Influence of barley variety and malting process on lipid content of malt

The lipid content of a beer affects its ability to form a stable head of foam and plays an important role in beer staling. The concentration and the quality of lipids in beer depend on their composition in the raw materials and on the brewing process and they may exert considerable influence on beer quality. This paper presents an investigation of the influence of barley variety and malting process on the lipid content of finished malt. Five barley samples, grown in Italy, representing 4 spring barley and 1 winter barley were used. The samples were micro-malted and analysed. The aim of this research was to verify the influence of different barley varieties on the lipid content of malt and also on the changes in fatty acid (FA) profile during the malting process. Lipid content and FA profile were evaluated. Principal component analysis (PCA) was used to establish relationships between the different samples. An evaluation of the correlation between lipid content of barleys and the quality of the resulting malts was also conducted. The data showed that the total lipid content during the malting process decreased significantly as barley was converted into malt. Different barley varieties present different FA contents and different FA patterns. The correlation between the lipid content of barley and the quality of the resulting malt confirmed the negative influence of lipids.

Effects of malting on molecular weight distribution and content of water-extractable β-glucans in barley

In the beer industry β-glucans are extensively studied non-starch polysaccharides due to their ability to increase the viscosity of solutions and to form gels. The current study was designed to determine the total and water-soluble β-glucan contents of barley during malting. Total and water-soluble β-glucans were analyzed from two different malts that originated from the same barley but varied in germination time from 36h (malt A) to 72h (malt B). Water-soluble β-glucans were also characterized using high-performance size-exclusion chromatography with triple-detector analysis (HPSEC-TDA) to evaluate the variation in molecular weight distributions, intrinsic viscosity, radius of gyration, Mark-Houwink parameters and polydispersity and thus the overall structural changes during malting. Total β-glucan content decreased from barley to malt due to the action of β-glucanase and was greatest in malt B (where 92% of β-glucans were degraded) which highlights the influence of germination time. β-Glucan solubility increased during malting, again particularly in malt B, where most of β-glucans became soluble. The β-glucanase activity also affected the molecular weight of the polymers which ranged from 298·103g/mol in barley to 293·103 and 218·103g/mol in malts A and B respectively. The molar mass of the most abundant fraction decreased from barley (256·103g/mol) to malt A (112·103g/mol) and malt B (89·103g/mol), again highlighting the effect of the longer germination time. Proceeding from barley to malt, the cumulative molar mass distribution function confirmed that the weight fraction of polymers below 200·103g/mol increased, while the high molecular weight fraction (between 200·103g/mol and 400·103g/mol) decreased. Moreover, the presence of a higher molecular weight fraction (14-16%) beyond 400·103g/mol which does not change during malting was observed. The Mark-Houwink constants α and log k confirmed the random coil conformation of soluble β-glucans and showed an increase in the compactness of the macromolecules from barley to malts.

Rapid determination of total fats and fat-soluble vitamins in Parmigiano cheese and salami by SFE

Abstract Supercritical fluid extraction (SFE) was used to determine total fat and fat-soluble vitamins in Parmigiano cheese and salami. Extracts were obtained quickly and effectively to gravimetrically determine total fat. The results were compared with traditional methods and the quantity extracted and collected by supercritical carbon dioxide (SC-CO2) was statistically equivalent to the Soxhlet extraction. In addition, the use of SFE as a preparative analysis was tested to determine in a rapid and simultaneous way the fat-soluble vitamin extracted by SFE and subsequently determined by HPLC. The extractability of vitamins by SFE was comparable to the official methods. α-tocopherol was higher probably because SC-CO2 extraction is necessarily conducted in the absence of light and oxygen, and lower temperature than traditional methods. RSD% was lower than 20% for total fat determination, while it was sometimes higher for fat-soluble vitamins determination.

Effects of Operating Conditions during Low-Alcohol Beer Production by Osmotic Distillation.

Osmotic distillation (OD) is a membrane technology most commonly used for liquid concentration, but recently there has been an increased interest in ethanol removal from alcoholic beverages. The aim of this paper is to investigate the effect of the variation of some operating conditions (temperature, flow rate, type and amount of stripping solution), specifically in regard to the effect on quality and sensory properties of the dealcoholized beers. The results indicated that temperature and flow rate variation showed no significant effect, whereas stripping solution variation had substantial effects mainly in terms of the ethanol removed. A cost appraisal showed that the operating costs were high mainly because of the cost of the stripping water. However, it is important to consider the final stripping solution, which is slightly alcoholic and enriched in flavor. For this reason, it could be reused in the manufacture of beverages, for instance as high gravity beer dilution water.

Influence of barley variety, timing of nitrogen fertilisation and sunn pest infestation on malting and brewing.

BACKGROUND This paper presents a multivariate approach to investigate the influence of barley variety, timing of nitrogen fertilisation and sunn pest infestation on malting and brewing. Four spring and two winter barley varieties were grown in one location in southern Europe. Moreover, one of the spring varieties was infested with sunn pest, in order to study the effects of this pest on malting quality, and subjected to different nitrogen fertilisation timing regimes. The samples were micromalted, mashed, brewed and analysed. RESULTS The data showed that even though the two winter barleys seemed to be the best regarding their physical appearance (sieving fraction I + II > 82%), this superiority was not confirmed in the malt samples, which showed low values of Hartong extract (27.1%) and high values of pH (6.07-6.11) and β-glucan content (12.5-13.2 g kg(-1)), resulting in low-quality beers. The barley sample subjected to postponed fertilisation had a total nitrogen content (19.5 g kg(-1) dry matter) exceeding the specification for malting barley and gave a beer with a low content of free amino nitrogen (47 mg L(-1)) and high values of viscosity (1.99 cP) and β-glucan content (533 mg L(-1)). The beer obtained from the barley sample subjected to pest attack had good quality parameters. CONCLUSION All spring barleys gave well-modified malts and consequently beers of higher quality than the winter barleys. Moreover, postponed fertilisation was negatively related to the quality of the final beer, and sunn pest infestation did not induce important economic losses in the beer production chain.

Internal and external validation strategies for the evaluation of long-term effects in NIR calibration models.

Some of the practical aspects of long-term calibration-set building are presented in this study. A calibration model able to predict the Kolbach index for brewing malt is defined, and four different validations and resampling schemes were applied to determine its real predictive power. The results obtained demonstrated that one single performance criterion might be not sufficient and can lead to over- or underestimation of the model quality. Comparing a simple leave-one-sample-out cross-validation (CV) with two more challenging CVs with leave-N-samples-out, where the resamplings were repeated 200 times, it is demonstrated that the error of prediction value has an uncertainty, and these values change according to the type and the number of validation samples. Then, two kinds of test-set validations were applied, using data blocks based on the sample collections year, demonstrating that it is necessary to consider long-term effects on NIR calibrations and to be conservative in the number of factors selected. The conclusion is that one should be modest in reporting the prediction error because it changes according to the type of validation used to estimate it and it is necessary to consider the long-term effects.

Secoisolariciresinol diglucoside determination in flaxseed (Linum usitatissimum L.) oil and application to a shelf life study

A high-performance liquid chromatographic (HPLC) reliable and sensitive method with diode array detection (DAD) system has been developed for the determination of secoisolariciresinol diglucoside (SDG) in flaxseed oil. An analytical methodology based on the sample extraction with methanol/water (80:20, v/v), subsequent purification of the sample and analysis of the extract by HPLC/DAD is proposed for the determination of SDG in flaxseed oil. The coefficient of determination of the standard calibration curve was 0.999, the limit of detection was 0.08μg/mL, and the limit of quantification was 0.27μg/mL. The recovery test was conducted adding four different concentrations of standard solution to the blank sample. The recovery ranged from 90% to 95%. To our knowledge, the presence and quantification of SDG in flaxseed oil has never been reported. The proposed method was tested to study the variation in SDG content in flaxseed oil during a shelf-life test to verify its applicability in quality control for oil industries. The dark and the low temperature of storing together allowed to preserve SDG. A slight pro-oxidant effect was observed for the addition of antioxidant to the flaxseed oil.

Evaluation of different validation strategies and long term effects in NIR calibration models.

Stable and reliable NIR calibration models for the barley malt quality assessment were developed and exhaustively evaluated. The measured parameters are: fine extract, fermentability, pH, soluble nitrogen, viscosity, friability and free-amino nitrogen. The reliability of the developed calibration models was evaluated comparing the classic leave-one-out internal validation with a more challenging one exploiting re-sampling scheme. The long-term effects, intended as possible alterations of the NIR method predictive power, due to the variation between samples collected in different years, were evaluated through an external validation which demonstrated the stability of the developed calibration models. Finally, the accuracy and the precision of the developed calibration models were evaluated in comparison with the reference methods. This exhaustive evaluation offers a realistic idea of the developed NIR methods predictive power for future unknown samples and their application in the beer industry.