Special Issue on Application of Instrumental Methods for Food and Food By-Products Analysis

1. Introduction

The application of various analytical procedures and methods determining the properties and safety of food and food constituents is a particularly important topic when dealing with food and food by-product analyses. Advanced analytical tools are of great importance for food quality determination, including the chemical and physicochemical characteristics, thermal properties and stability of food products, and recently also the by-products of the food industry. Thanks to the use of instrumental methods it is also possible to investigate innovative, newly formulated food products and technologies.

Taking the aforementioned reasons into account, this Special Issue aims to collect information and results dealing with procedures, instrumental analytical techniques and methods that are applied to study food and food processing by-products. A discussion of the application of advanced methods in food research to detect and characterize specific food components of significance to food science and technology, such as lipids, proteins, and carbohydrates seems to be of significant importance.

In total, there were 14 manuscripts submitted to this Special Issue, 13 of which were published. The articles belong to two main groups: (i) instrumental methods used in food analysis; (ii) innovative procedures enabling bioactive compounds and oil extraction from by-products.

2. Instrumental Methods Used in Food Analysis

Three of the published manuscripts are concerned with an analysis of oil and fat fraction by using advanced techniques.

The article titled “Phytochemical Profile of Eight Categories of Functional Edible Oils: A Metabolomic Approach Based on Chromatography Coupled with Mass Spectrometry” published by Carmen Socaciu and coauthors [1] aimed to define the influence of botanical origins on the phytochemical components of 30 edible oils from eight categories and to define their specific identity biomarkers. Advanced techniques based on gas and liquid chromatography coupled with diode array, mass spectrometry, or fluorescence detection were very helpful in the study of fatty acids, volatiles, carotenoids, tocopherols, and phenolic components. Taking into account the obtained results, the specific recognition biomarkers were defined and a so called “identity card” was proposed for each category of oil. The results of investigations demonstrated that the application of instrumental methods combined with chemometric models can be helpful to determine the oils’ botanical origin based on the studies of qualitative and quantitative differences between samples. In the study of Wirkowska M. and coauthors [2], chromatographic and thermal methods were applied to characterize oils isolated from quinoa and amaranth seeds. The oxidative stability was determined by using pressure differential scanning calorimetry and the Rancimat test and the kinetic parameters of the oxidation process were determined using differential scanning calorimetry. Additionally, differential scanning calorimetry was applied to define the melting characteristics of oils and gas chromatography was employed for an analysis of the fatty acid composition and their distribution in triacyglycerols. Based on the obtained results, the authors stated that both types of seeds can be a good source of unsaturated fatty acids. Taking into account the values of the induction time of oxidation, it can be suggested that quinoa oil presents worse resistance to oxidation than amaranth oil. The melting characteristics of the oils confirmed the presence of low-melting triacylglycerol fractions with unsaturated fatty acids. The authors concluded that the obtained results of the kinetics of the oxidation reaction can be useful to predict the oxidation process under various conditions and may be helpful when assessing the oxidation rate of oils from other pseudocereals. In the manuscript titled “Lipid Fraction Properties of Homemade Raw Cat Foods and Selected Commercial Cat Foods” published by Górska A. and coauthors [3], lipid fractions from five self-prepared and seven commercial cat foods were characterized using gas chromatography in order to define the composition of fatty acids and the pressurized differential scanning calorimetry technique was used to determine oxidative stability. Based on the obtained results, the authors stated that self-prepared cat foods contained a high level of essential fatty acids but showed low oxidative stability, especially for those with significant amounts of polyunsaturated fatty acids. It was found that the omega-6 to omega-3 fatty acids ratio was beneficial, despite the low amount of essential fatty acids. Furthemore, in the case of fats extracted from commercial cat foods a longer induction time was determined in comparison to fats isolated from self-prepared samples, indicating higher oxidative stability of fats. The authors also pointed out that the distribution of fatty acids in the triacylglycerol structure for cat food was determined in their article for the first time.

Four of published articles were focused on an investigation of new products and the impact of applied processing technologies on food-sample properties by using advanced analytical tools.

In the article titled “The Influence of a Chocolate Coating on the State Diagrams and Thermal Behaviour of Freeze-Dried Strawberries” authored by Ostrowska-Ligęza E., Szulc K., Jakubczyk E., Dolatowska-Żebrowska K., Wirkowska-Wojdyła M., Bryś J. and Górska A. [4], DSC curves, sorption isotherms, glass transition temperature and state diagrams of freeze-dried strawberries and dark and milk chocolate coated freeze-dried strawberries were determined. The obtained results allowed them to conclude that the shape and course of the sorption isotherms of the freeze-dried strawberries and dark and milk chocolate-coated strawberries were influenced by the method of snack preparation. It is worth mentioning that after coating with milk or dark chocolate changes in the hygroscopicity tendency of the freeze-dried strawberries, a significant reduction was observed. Such behaviour can consequently result in improving the shelf life of a final product. In the study of Jakubczyk E. and coauthors [5], the influence of the addition of apple puree and maltodextrin to agar sol on the sorption properties and structure of the dried gel was determined. Additionally, different drying methods were used to determine their effect on the sorption behaviour of apple puree gels. Among the analyzed samples, the air-dried apple puree gels were considered as producing the lowest hygroscopicity and the highest stability at room conditions. In addition, changes in sample composition, namely a decrease in the amount of apple puree from 40 to 25% in dried gels, improved the sorption properties. Based on the obtained results, the authors stated that it is possible to obtain new products with a tailored structure and sorption properties by designing a composition of products and via the application of certain drying methods. In the article titled “Sous Vide Cooking Effects on Physicochemical, Microbiological and Sensory Characteristics of Pork Loin”, Kurp L. and coauthors [6] aimed to study the characteristics (cooking loss, instrumentally measured colour and texture, microbiological quality and sensory properties) of pork loin and the influence of different temperature-time combinations applied in sous vide pork cooking. Based on the obtained results, it was concluded that in the case of cooking at 60 or 65 °C for 4 h, pork loin showed the most attractive and acceptable sensory traits. Texture attributes were thought to be of most importance for pork perception. Sous vide processing of meat at 60 °C/4 h caused less cooking loss than at 65 °C/4 h, however, this was not confirmed for moisture content and sensorially assessed juiciness. Authors showed that the applied parameters of sous vide cooking were sufficient to reduce the microflora in the pork loin to the level safe for consumption. In the next article published by Bingman M. and coauthors [7], the profile of volatile organic compounds from pressed apple juice, processed through fermentation and dry hopping was monitored by Headspace-Solid Phase Microextraction-Gas Chromatography-Mass Spectrometry analysis in order to define the process of the occurrence of aroma compounds in cider production. It is worth mentioning that 89 volatile organic compounds, such as higher alcohols, acetate esters, ethyl esters, other esters, aldehydes, ketones, volatile acids, and terpenes were detected throughout processing. The authors reported that both the variety of hops and the time taken to complete key processing steps significantly influence the profile and concentration of aroma-important volatile organic compounds in dry-hopped cider.

In this Special Issue, a group of articles are provided that aim to study certain food ingredients, components and additives that can affect the quality of the final products.

In the article titled ”The Effect of Essential Oils on the Survival of Bifidobacterium in In Vitro Conditions and in Fermented Cream”, Kozłowska and coauthors [8] performed an in vitro study investigating how the viability of selected Bifidobacterium strains is influenced by the presence of essential oils extracted from clove buds, lemon peels, and juniper berries. The authors also studied, using cream samples during fermentation and after storage, the effect of the addition of selected essential oils on the viability of the Bifidobacterium strain. The solid-phase microextraction (SPME)-GC–time-of-flight (TOF)-MS method was used to determine the volatile aroma compound profiles of sour cream samples with essential oils. In their in vitro study, the authors found that the studied strains of Bifidobacterium were sensitive to the influence of the selected essential oils. Among the tested strains of the genus Bifidobacterium, B. animalis subsp., lactis Bb-12 showed the most sensitive behavior when essential oils of clove and juniper were applied. Additionally, there was no influence of the concentration and type of essential oils on the number of cells of this strain in the cream samples after fermentation and after 21-day storage. The authors pointed out that the tested essential oils could be added to dairy products as natural substances, thereby enriching sensory attributes and health-promoting properties. In the study of Kasapidou E. and coauthors [9], the possibility of near infrared reflectance spectroscopy application for the estimation of the chemical composition of traditional sausages was tested. The obtained results of the calibration model revealed that near infrared reflectance spectroscopy can be useful in the traditional village-style sausages analysis including in terms of fat content, with very good precision. Moisture and protein content can be assessed with the application of this method with good accuracy. Additionally, the authors concluded that the external validation confirmed the ability of near infrared reflectance spectroscopy to predict the chemical composition of sausages and that the method can be applied as a screening technique when a high but not an absolute level of accuracy is required. Methods and systems for determining the lycopene content in fruits were presented by Villaseñor-Aguilar M.J. and coauthors [10]. The authors pointed out that among the optical systems focused on the estimation and identification of lycopene are high-performance liquid chromatography, the colorimeter, infrared near NIR spectroscopy, UV-VIS spectroscopy, Raman spectroscopy, and the systems of multispectral imaging and hyperspectral imaging. Based on the literature analysis, it was summarized that high-performance liquid chromatography and spectrophotometry methods can provide more efficient results, but they present some limitations due to long and complicated measurement procedures. On the other hand, multispectral, hyperspectral, and colorimeter imaging techniques are characterized as fast, non-contact and suitable for online applications but still require further study regarding their accuracy. Other methods such as NIR spectroscopy, UV-Vis spectroscopy, and Raman spectroscopy have proven to be moderately reliable with respect to high-performance liquid chromatography. According to authors, it is worth mentioning that the introduction of artificial intelligence algorithms, the internet of things, parallel processing hardware, and the reduction of equipment costs are areas of future study that can lead to the early translation of laboratory results to field applications.

The development of effective methods that can be used in the effective separation of active compound from certain mediums is an important topic in food technology. This problem was discussed by Małajowicz J. and coauthors [11] in their study verifying the possibility of secreting gamma-decalactone separation from biotransformation media, in which a lactone was synthesized from castor oil via Yarrowia lipolytica KKP379 yeast. The effectiveness of the following three techniques: liquid–liquid extraction, hydrodistillation and adsorption was compared with regard to fragrance recovery. Based on the obtained results, and by taking into account the selectivity of the process, its efficiency, and the speed of execution, adsorption on Amberlite XAD-4 can be recommended. In the context of the purity of the released gamma-decalactone, the hydrodistillation process seems to be more advantageous. According to the authors, it is worth mentioning that the effect of many factors should be considered before choosing a proper separation method. It should be concluded that the development of an effective method of gamma-decalactone separation from biotransformation media seems to be important in the context of the attempts to apply a biotechnological synthesis of peach lactone in industry.

In the article published by Wierzchowska K. and coauthors [12] they attempted to study the efficiency of microbial oil production, fatty acid composition and the growth of Y. lipolytica yeast, influenced by inorganic phosphorus and nitrogen sources limitations. The authors highlighted the importance of nitrogen limitation in culture media. It is worth mentioning that further phosphorus limitation may consequently lead to the higher efficiency of microbial lipid biosynthesis. According to the authors, the phosphorus and nitrogen level as well as the ratio should be taken into account as one of the important factors that influences microbial lipid production and satisfactory biomass yield. Interestingly, the authors pointed out that such approaches seem to be practically essential when the possibility of the use of oily waste as a substrate in microbial culture is discussed.

3. Alternative Methods of Bioactive Compounds and Oil Extraction from By-Products

By-products of the food industry can be considered as a source of valuable bioactive substances and oils with the potential of reuse, so it is of urgent need to search for novel extraction methods that may help to obtain extracts or oils with improved properties. Particularly, Piasecka and coauthors [13], in the article titled “Alternative Methods of Bioactive Compounds and Oils Extraction from Berry Fruit By-Products—A Review” summarized possible extraction methods, including alternative, innovative techniques and their impact on the composition of extracts and oils obtained from berry fruit by-products. In the article, it was pointed out that application of conventional solvent extraction techniques may present the disadvantage of being insufficient in the achievement of high polyphenol or lipid fraction yields and in the selective isolation of characteristic compounds. The authors further indicated the significance of alternative extraction methods such as ultrasound-assisted extraction, pulsed electric field-assisted extraction, microwave-assisted extraction and supercritical fluid extraction as possible ways by which to improve the efficiency of the isolation of bioactive compounds and oils from berry fruit by-products. It is of great importance that these non-conventional techniques are classified as green extraction methods due to the lower energy, solvent volume and time consumption. In the article, the authors pointed out major differences between the applied methods with respect to their usefulness. Additionally, important factors such as the selection of solvents and solid–liquid ratios used in the extraction process were discussed. The time required for the extraction process is another important factor that was different across the studied methods. By applying alternative extraction methods such as ultrasound-assisted extraction or microwave-assisted extraction, the time required for extraction processes can be reduced in comparison to traditional solid–liquid extraction.