Natural Standard: Variability of Techno-Chemical Indicators of Traditional Guba Apple Varieties and Direct-Pressed Juices
This three-year study of traditional Guba apple varieties in Azerbaijan's Guba-Khachmaz region reveals that local cultivars like Shikha Jana and Sarah Tursh exhibit superior climate adaptation and juice yields compared to global varieties, while also documenting significant biochemical degradation during storage to establish natural quality fluctuation boundaries for food industry and breeding applications.
Original paper licensed under CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). This is an AI-generated explanation of the paper below. It is not written or endorsed by the authors. For technical accuracy, refer to the original paper. Read full disclaimer
In the foothills of the Guba-Khachmaz region in Azerbaijan, a unique microclimate shaped by the nearby Caspian Sea and specific soil conditions creates a natural laboratory for growing fruit. Here, the apples that grow are not just food; they are a record of their environment, carrying a chemical signature that changes as they ripen on the tree and as they sit in storage. To understand what makes a fruit valuable, scientists look at its internal chemistry. They measure how much sugar is dissolved in the fruit's juice, how much acid gives it a tart bite, and how much vitamin C it holds. They also track how much water the fruit loses over time, which concentrates these flavors, and how easily the fruit releases its juice when pressed. This balance of sweetness, tartness, and moisture determines whether an apple is best eaten fresh, stored for months, or turned into juice. For the food industry, knowing these exact limits is crucial. It helps producers avoid adding artificial sugar or acid to their products and ensures that the juice they sell is truly what it claims to be. Without this deep understanding of how local varieties behave, it is impossible to distinguish a genuine, high-quality product from a fake one or to know which apples will survive the long journey from the tree to the consumer's table.
A team of researchers from the Research Institute of Fruit and Tea Growing in Azerbaijan set out to map these natural changes in thirteen different types of apples grown in the Guba district. They focused on a mix of ancient local varieties that have been grown there for generations, such as Gara Tursh and Shihi Janı, alongside famous global commercial types like Golden Delicious and Starkrimson. The scientists watched these trees over three years, from 2021 to 2023, taking samples at two critical moments: first in early August when the fruit was still developing, and again in late October when the apples were fully ready to be harvested. They did not just weigh the fruit; they crushed it to measure the exact amount of sugar, acid, and vitamin C in the juice, and they pressed the fruit to see how much liquid could be extracted. They then stored a selection of these apples for five months in a warehouse with natural ventilation, where the temperature slowly dropped from a mild autumn warmth to a cool winter chill, to see how the fruit's chemistry changed over time without the help of expensive refrigeration technology.
The study revealed that every apple variety follows its own distinct path as it matures. By late October, the researchers found that the local varieties had adapted perfectly to the region's climate. The Shihi Janı and Sary Tursh apples, for instance, reached a state where they held an ideal balance of sugar, acid, and water. When these specific local apples were pressed, they yielded an exceptional amount of juice, with nearly eighty percent of the fruit's weight turning into liquid. This is a very high number, indicating that the fruit's cells are full of water and break down easily under pressure. In contrast, the popular Starkrimson variety, while large and attractive, performed poorly in this regard. By the time it was fully ripe, its flesh had become soft and mealy, trapping the juice inside. When pressed, it yielded less than sixty percent juice, meaning a significant portion of the fruit's weight was wasted as dry pulp. This difference showed that while global varieties are often chosen for their size and appearance, the local ancient varieties are superior for making juice because their internal structure releases liquid much more efficiently.
The chemical makeup of the fruit also shifted dramatically as the season progressed. In most apples, the starch stored in the fruit during the summer breaks down into simple sugars as the apple ripens, making it sweeter. The researchers observed that the local Gara Tursh and Jir Gadzhi varieties actually increased their total dry matter content as they hung on the tree, suggesting they were actively pulling nutrients from the leaves even late in the season. However, the most striking changes occurred during the five-month storage period. As the apples sat in the warehouse, they continued to breathe, consuming their own energy reserves. This process caused a significant drop in vitamin C and acidity across all varieties. The loss was not uniform; some varieties held their nutrients better than others. The Rosmarina Bianc apple lost the least amount of vitamin C, retaining more than half of its original content, while the Sary Tursh variety lost almost all of its vitamin C, dropping by nearly ninety-five percent. Similarly, the acidity of the Reinette Simirenko apple plummeted by more than eighty percent, making it much milder in flavor, whereas the Sary Tursh apple held onto its tartness much better, losing only about twenty-four percent of its acid.
These findings highlight that the "best" apple depends entirely on what the grower intends to do with it. If the goal is to produce fresh juice or concentrate, the local varieties like Reinette de Champagne and Shihi Janı are superior because they release so much liquid and start with a high concentration of natural sugars, often exceeding the international standard for apple juice. If the goal is to store fruit for a long time without it losing its tart bite, the Sary Tursh variety is the clear winner. However, if the priority is preserving vitamin C, the Rosmarina Bianc is the most resilient. The study confirms that these traditional, locally adapted varieties are not just relics of the past but are scientifically valuable resources. They possess unique chemical profiles that modern, mass-produced varieties often lack, offering a natural solution for producing high-quality food products that are both authentic and efficient. By understanding these specific behaviors, producers can choose the right apple for the right job, ensuring that the rich harvest of the Guba region is used to its fullest potential.
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