Fruit juice is made from a wide variety of fruits, including oranges, apples, grapes, cranberries, grapefruits, tomatoes, bayberries, and pineapples. In the United States, the term “fruit juice” can only be legally used to describe a product which is 100% fruit juice. A blend of fruit juice with other ingredients is referred to as a “juice cocktail” or “juice drink.” Sugar is an important constituent of any fruit juice and while labels may say “No Added Sugar,” the product may contain large amounts of naturally occurring sugars, and this must be noted on the product label with other carbohydrates. Beverages listed as 100% juice may also contain unlisted additives. The suffix “ade” refers to dilution with water and sugar if fruit juice is too sour, rich, or acidic to consume. Examples of this include lemonade and limeade.
Fruit Juice Manufacturing
The first step in making fruit juice is to wash and sort the food source. It is prepared by mechanically squeezing or macerating the fruit without the application of heat or solvents. This process can be referred to as “cold-pressed.” There are typically two automated methods that are used for this process. One method uses two metal cups with sharp metal tubes on the bottom cup that come together, which removes the peel of the fruit and forces the flesh through the metal tube. There are small holes in the tube that allow the juice to escape and be collected. The other method requires fruits to be cut in half and the juice is extracted using reamers. Most juices are filtered after extraction to remove fiber or pulp. One notable exception is orange juice, which is sold pulp-free as well as with various levels of pulp. After filtration, juices can be concentrated in evaporators if desired. Concentrated juices are heated under a vacuum to remove water and then cooled to around 13°C, removing around two-thirds of the water in the process. Concentrated juice is easier to transport and has an increased shelf life. It may be reconstituted with water or sold directly in the concentrated state. Pasteurization is used to inactivate enzymes and destroy any spoilage microbes. This normally consists of a continuous system that has a heating zone, hold tube, and cooling zone, after which the juice is packaged. High intensity pulsed electric fields have emerged as an alternative to traditional pasteurization, and this method maintains better quality while performing the same tasks required for pasteurization.
There are many important constituents to measure in fruit juice, and NIR spectroscopy has been examined as a potential tool to replace traditional time-consuming and expensive methods. Sugar and acidity measurements are the most important constituents and are strictly regulated in marketed juices. Sugars such as glucose, fructose, and sucrose are essential quality control parameters in fruit juices. Soluble Solids Content (SSC, expressed as °Brix) is one of the primary characteristics used to determine the sweetness of fresh and processed fruit products. Titratable Acidity (TA) is related to the organic acid contents. It is a measurement of color stability and the shelf life of fruit and its processed products. These sugar and acidity constituents have all been studied using NIR spectroscopy as an analytical tool with excellent results. In the case of glucose, sucrose, and fructose, calibration models created from stock standards were able to measure the concentration of these sugars in both apple and orange juice.
NIR spectroscopy can provide an online method for real-time process control of these parameters as well as monitor for adulteration and contamination. As is the case with all food products, adulteration is a major problem for fruit processed products. Adulteration can take on many forms including the addition of cheaper quality juice or artificial sweeteners. NIR spectroscopy has been examined for juice discrimination as well for adulteration using saccharin with excellent results. This type of analysis also shows the potential for analyzing blend profiles in fruit juices. Proper storage of fruit juice is important as well because improper storage leads to oxidation, producing undesired physiochemical changes. Such changes directly affect both pH and SSC and NIR spectroscopy has shown the potential to monitor stored fruit juice for quality by monitoring these parameters. NIR spectroscopy can be used to monitor parameters of interest in fruit juice and has the potential to replace traditional methods. And although more work and study are required, it is a potential replacement for both laboratory and online traditional quality control methods in the fruit juice industry. Advancements in application development and online analysis continue to move forward to realize the potential of NIR spectroscopy as a method for real-time, online implementation as a process control tool.
Quality Analysis, Classification, and Authentication of Liquid Foods by Near-Infrared Spectroscopy: A Review of Recent Research Developments – Wang, Sun, Pu, and Cheng, Critical Reviews in Science and Nutrition, 2017, Vol. 57, No. 7, 1524-1538
Rapid Analysis of Sugars in Fruit Juices by FT-NIR Spectroscopy – Rodriguez-Saona, Fry, McLaughlin, Calvey, Carbohydrate Research 336 (2001) 63-74 https://www.sciencedirect.com/science/article/abs/pii/S0008621501002440
Measurement of Soluble Solids Contents and pH in Orange Juice Using Chemometrics and Vis-NIRS – Cen, He, Huang, Journal of Agricultural and Food Chemistry, 2006, 54, 7437-7443
Applications of FT-NIRS Combined With PLS Multivariate Methods For the Detection & Quantification of Saccharin Adulteration in Commercial Fruit Juices – Mabood, Hussain, Jabeen, Food Additives, and Contaminants: Part A, 2018, Vol. 35, No. 6, 1052-1060